Anatomy and physiology of the brain and spinal cord

The brain is a spongy organ made up of nerve and supportive tissues. It is

located in the head and is protected by a bony covering called the skull. The base, or

lower part, of the brain is connected to the spinal cord. Together, the brain and spinal

cord are known as the central nervous system (CNS). The spinal cord contains nerves

that send information to and from the brain. The CNS works with the peripheral nervous

system (PNS). The PNS is made up of nerves that branch out from the spinal cord to

relay messages from the brain to different parts of the body. Together, the CNS and

PNS allow a person to walk, talk, throw a ball and so on.

Structure and function of the brain

The brain is the body’s control centre. It constantly receives and interprets nerve

signals from the body and responds based on this information. Different parts of the

brain control movement, speech, emotions, consciousness and internal body functions,

such as heart rate, breathing and body temperature.

The brain has 3 main parts: cerebrum, cerebellum and brain stem.

Cerebrum

The cerebrum is the largest part of the brain. It is divided into 2 parts (halves)

called the left and right cerebral hemispheres. The 2 hemispheres are connected by a

bridge of nerve fibres called the corpus callosum. The right half of the cerebrum (right

hemisphere) controls the left side of the body. The left half of the cerebrum (left

hemisphere) controls the right side of the body.

 

The outer surface of the cerebrum is called the cerebral cortex or grey matter. It

is the area of the brain where nerve cells make connections, called synapses, that

control brain activity. The inner area of the cerebrum contains the insulated (myelinated)

bodies of the nerve cells (axons) that relay information between the brain and spinal

cord. This inner area is called the white matter because the insulation around the axons

gives it a whitish appearance.

 

The cerebrum is further divided into 4 sections called lobes. These include the frontal

(front), parietal (top), temporal (side) and occipital (back) lobes.

Each lobe has different functions:

The frontal lobe controls movement, speech, behaviour, memory, emotions and

intellectual functioning, such as thought processes, reasoning, problem solving,

decision making and planning. The parietal lobe controls sensations, such as touch,

pressure, pain and temperature. It also controls spatial orientation (understanding of

size, shape and direction). The temporal lobe controls hearing, memory and emotions.

The left temporal lobe also controls speech.The occipital lobe controls vision.

Cerebellum

The cerebellum is the next largest part of the brain. It is located under the cerebrum at

the back of the brain. It is divided into 2 parts or hemispheres and has grey and white

matter, much like the cerebrum. The cerebellum is responsible for: movement, posture,

balance, reflexes, complex actions (walking, talking), collecting sensory information

from the body

Brain stem

The brain stem is a bundle of nerve tissue at the base of the brain. It connects the

cerebrum to the spinal cord and sends messages between different parts of the body

and the brain.The brain stem has 3 areas: midbrain, pons, medulla oblongata.

The brain stem controls breathing, body temperature, blood pressure, heart rate, hunger

and thirst.

Cranial nerves emerge from the brainstem. These nerves control facial sensation, eye

movement, hearing, swallowing, taste and speech.

Other important parts of the brain

Cerebrospinal fluid (CSF)

The cerebrospinal fluid (CSF) is a clear, watery liquid that surrounds, cushions and

protects the brain and spinal cord. The CSF also carries nutrients from the blood to, and

removes waste products from, the brain. It circulates through chambers called ventricles

and over the surface of the brain and spinal cord. The brain controls the level of CSF in

the body.

Meninges

The brain and spinal cord are covered and protected by 3 thin layers of tissue

(membranes) called the meninges: dura mater – thickest outer layer, arachnoid layer –

middle, thin membrane, pia mater – inner, thin membrane.

 

CSF flows in the space between the arachnoid layer and the pia mater. This space is

called the subarachnoid space. The tentorium is a flap made of a fold in the meninges.

It separates the cerebrum from the cerebellum.

The supratentorial area of the brain is the area above the tentorium. It contains the

cerebrum, the first and second (lateral) ventricles, the third ventricle, and glands and

structures in the centre of the brain. The infratentorial area is located at the back of the

brain below the tentorium. It contains the cerebellum and brain stem. This area is also

called the posterior fossa.

Corpus callosum. The corpus callosum is a bundle of nerve fibres between the 2

cerebral hemispheres. It connects and allows communication between both

hemispheres.

Thalamus. The thalamus is a structure in the middle of the brain that has 2 lobes or

sections. It acts as a relay station for almost all information that comes and goes

between the brain and the rest of the nervous system in the body.

Hypothalamus. The hypothalamus is a small structure in the middle of the brain below

the thalamus. It plays a part in controlling body temperature, hormone secretion, blood

pressure, emotions, appetite, and sleep patterns.

Pituitary gland. The pituitary gland is a small, pea-sized organ in the centre of the

brain. It is attached to the hypothalamus and makes a number of different hormones

that affect other glands of the body’s endocrine system. It receives messages from the

hypothalamus and releases hormones that control the thyroid and adrenal gland, as

well as growth and physical and sexual development.

Ventricles. The ventricles are fluid-filled spaces (cavities) within the brain. There are 4

ventricles: The first and second ventricles are in the cerebral hemispheres. They are

called lateral ventricles. The third ventricle is in the centre of the brain, surrounded by

the thalamus and hypothalamus. The fourth ventricle is at the back of the brain between

the brain stem and the cerebellum. The ventricles are connected to each other by a

series of tubes. The fluid in the ventricles is cerebrospinal fluid (CSF). The CSF flows

through the ventricles, around the brain in the space between the layers of the

meninges (subarachnoid space) and down the spinal cord.

Pineal gland. The pineal gland is a very small gland in the third ventricle of the brain. It

produces the hormone melatonin, which influences sleeping and waking patterns and

sexual development.

Choroid plexus. The choroid plexus is a small organ in the ventricles that makes CSF.

Cranial nerves. There are 12 pairs of cranial nerves that perform specific functions in

the head and neck area. The first pair starts in the cerebrum, while the other 11 pairs

start in the brain stem. Cranial nerves are indicated by number (Roman numeral) or

name.

 

Cranial nerves and their functions

Number Name Function

I olfactory smell

II optic vision and light detection by the pupil

III oculomotor eye movement upward, downward or inward

narrowing and widening of the pupil

lifting of the eyelid

IV trochlear eye movement downward and inward

V trigeminal facial sensation

chewing

VI abducens outward eye movement

VII facial facial expression

closing of the eyelid

taste in the front part of the tongue

VIII acoustic hearing

balance

IX glossopharyngeal swallowing

gag reflex

speech

X vagus swallowing

gag reflex

speech (vocal cords)

control of muscles in internal organs

XI accessory neck turning

shoulder shrugging

XII hypoglossal tongue movement

Blood-brain barrier. The blood-brain barrier is a specialized system of blood vessels

and enzymes that protect the brain from chemicals or toxins produced by bacteria. It

helps maintain a constant environment for the brain. The blood-brain barrier is made up

of very small blood vessels (capillaries) that are lined with thin, flat endothelial cells. In

other parts of the body, endothelial cells have small spaces between them that allow

substances to move in and out of the capillary so they can reach other cells and tissues.

In the brain, the endothelial cells are packed tightly together so substances cannot pass

out of the bloodstream into the brain. The enzymes also restrict the types of substances

that can be carried from the bloodstream into the brain. Some substances can pass

through the blood-brain barrier, such as very small molecules and molecules that can

be dissolved in fat (are lipid soluble).

Types of cells in the brain

The brain is made up of neurons and glial cells. Neurons, these cells carry the signals

that make the nervous system work. They cannot be replaced or repaired if they are

damaged. Glial cells (neuroglial cells), these cells support, feed and protect the

neurons. The different types of glial cells are: astrocytes, oligodendrocytes, ependymal

cells, microglial cells

Structure and function of the spine

The spine is made up of vertebrae, sacrum and coccyx – bony sections that house and

protect the spinal cord (commonly called the spine). The vertebral body is the biggest

part of a vertebra. It is the front part of the vertebra, which means it faces into the body.

Spinal cord is a column of nerves inside the protective vertebrae that runs from the

brain to the bottom of the spine. Disc is a layer of cartilage between each vertebra that

cushions and protects the vertebrae and spinal cord.

The spine is divided into 5 sections, the cervical – the vertebrae from the base of the

skull to the lowest part of the neck, thoracic – the vertebrae from the shoulders to mid-

back, lumbar – the vertebrae from mid-back to the hips, sacrum – the vertebrae at the

base of the spine. The vertebrae in this section are fused and do not flex. Coccyx – the

“tail bone” at the end of the spine. The vertebrae in this section are fused and do not

flex.

Spinal nerves. The spine relays messages between the body and the brain. These

nerve messages control body functions like movement, bladder and bowel control and

breathing. Each vertebra has a pair of spinal nerves that receive messages from the

body (sensory impulses) and send messages to the body (motor impulses). The spinal

nerves are numbered from the cervical spine to the sacral spine.

 

Spinal nerves and their functions

Number Part of

spine

Function

C1 to

C8

(8 pairs)

cervical send messages to the back of the head, neck, shoulders, arms,

hands and diaphragm

T1 to

T12

(12

pairs)

thoracic send messages to the chest, some back muscles and parts of the

abdomen

L1 to L5

(5 pairs)

lumbar send messages to the lower parts of the abdomen and the back,

some of the legs and some parts of the external genital organs

S1 to S5

(5 pairs)

sacral send messages to the thighs, lower parts of the legs, feet, most of

the external genital organs, the groin area, the bladder and the anal

sphincter

ANATOMY AND PHYSIOLOGY OF THE LUNG

The lungs are located in the chest and are part of the respiratory system. The lungs

take up most of the space inside the chest. The lungs are surrounded by the chest wall.

The chest wall is made up of the ribs and the muscles between the ribs. The lungs are

separated by the mediastinum, which contains the heart and other organs. Below the

lungs is the diaphragm, a thin muscle that separates the chest cavity from the abdomen.

Each lung is divided into lobes (sections): The left lung has 2 lobes, the heart sits in a

groove (cardiac notch) in the lower lobe. The right lung has 3 lobes and is slightly larger

than the left lung.

 

The trachea (windpipe) is the tube-shaped airway in the neck and chest. It divides into 2

tubes or branches called the main bronchi. One bronchus goes to each lung. The area

where each bronchus enters the lung is called the hilum.

 

The pleura is a thin membrane that covers the lungs and lines the chest wall. It protects

and cushions the lungs and produces a fluid that acts like a lubricant so the lungs can

move smoothly in the chest cavity. The pleura is made up of 2 layers, the inner

(visceral) pleura – the layer next to the lung, and the outer (parietal) pleura – the layer

that lines the chest wall. The area between the 2 layers is called the pleural space.

 

Each of the main bronchi divides or branches into smaller bronchi (which have small

glands and cartilage in their walls). These smaller bronchi eventually divide into even

smaller tubes called bronchioles (which have no glands or cartilage). At the end of the

bronchioles are millions of tiny sacs called alveoli. Surrounding the alveoli are very tiny

blood vessels (capillaries). The bronchi are lined with cells that have very fine hair-like

projections called cilia.

 

The lungs produce a mixture of fats and proteins called lung or pulmonary surfactant.

The surfactant coats the surfaces of the alveoli, making it easier for them to expand and

deflate with each breath.

 

Different groups of lymph nodes, which are part of the lymphatic system, drain fluid

normally produced in the lung, bronchial nodes – lymph nodes around the main bronchi,

hilar nodes – lymph nodes in the area where the trachea divides into the main bronchi,

upper (superior) mediastinal nodes – lymph nodes at the top of the mediastinum,

subcarinal mediastinal nodes – lymph nodes just below the trachea where it divides into

the main bronchi, lower (inferior) mediastinal nodes – lymph nodes at the bottom of the

mediastinum

Function

The main functions of the lungs are to transfer oxygen from the air to the blood and to

release carbon dioxide from the blood to the air. Air enters the mouth or nose and

travels through the trachea (windpipe), bronchi and bronchioles to the alveoli. The

exchange of oxygen and carbon dioxide takes place in the alveoli. The alveoli absorb

oxygen from the air and pass it into the blood, which circulates the oxygen around the

body. Carbon dioxide, which is a waste product of the body’s cells, passes from the

blood into the alveoli and is breathed out.

 

The lungs also play a role in the body’s defences against harmful substances in the air,

such as smoke, pollution, bacteria or viruses. These substances can pass through the

nose and become trapped in the lungs. The lungs produce a thick, slippery fluid

(mucus), which can trap and partly destroy these materials. The cilia move rapidly to

push the mucus up through the bronchi, where it is removed by coughing or swallowing.

CARDIOVASCULAR SYSTEM

The cardiovascular system consists of the heart, blood vessels, and the approximately 5

liters of blood that the blood vessels transport. Responsible for transporting oxygen,

nutrients, hormones, and cellular waste products throughout the body, the

cardiovascular system is powered by the body’s hardest-working organ — the heart,

which is only about the size of a closed fist. Even at rest, the average heart easily

pumps over 5 liters of blood throughout the body every minute.

CARDIOVASCULAR SYSTEM ANATOMY

The Heart 

The heart is a muscular pumping organ located medial to the lungs along the body’s

midline in the thoracic region. The bottom tip of the heart, known as its apex, is turned

to the left, so that about 2/3 of the heart is located on the body’s left side with the other

1/3 on right. The top of the heart, known as the heart’s base, connects to the great

blood vessels of the body: the aorta, vena cava, pulmonary trunk, and pulmonary veins.

Circulatory Loops

There are 2 primary circulatory loops in the human body: the pulmonary circulation

loopand the systemic circulation loop. Pulmonary circulation transports deoxygenated

blood from the right side of the heart to the lungs, where the blood picks up oxygen and

returns to the left side of the heart. The pumping chambers of the heart that support the

pulmonary circulation loop are the right atrium and right ventricle. Systemic circulation

carries highly oxygenated blood from the left side of the heart to all of the tissues of the

body (with the exception of the heart and lungs). Systemic circulation removes wastes

from body tissues and returns deoxygenated blood to the right side of the heart. The left

atrium and left ventricle of the heart are the pumping chambers for the systemic

circulation loop.

Blood Vessels 

Blood vessels are the body’s highways that allow blood to flow quickly and efficiently

from the heart to every region of the body and back again. The size of blood vessels

corresponds with the amount of blood that passes through the vessel. All blood vessels

contain a hollow area called the lumen through which blood is able to flow. Around the

lumen is the wall of the vessel, which may be thin in the case of capillaries or very thick

in the case of arteries.

All blood vessels are lined with a thin layer of simple squamous epithelium known as

the endothelium that keeps blood cells inside of the blood vessels and prevents clots

from forming. The endothelium lines the entire circulatory system, all the way to the

interior of the heart, where it is called the endocardium.

There are three major types of blood vessels: arteries, capillaries and veins. Blood

vessels are often named after either the region of the body through which they carry

blood or for nearby structures. For example, the brachiocephalic artery carries blood

into the brachial (arm) and cephalic (head) regions. One of its branches, the subclavian

artery, runs under the clavicle; hence the name subclavian. The subclavian artery runs

into the axillary region where it becomes known as the axillary artery.

Arteries and Arterioles: Arteries are blood vessels that carry blood away from the heart.

Blood carried by arteries is usually highly oxygenated, having just left the lungs on its

way to the body’s tissues. The pulmonary trunk and arteries of the pulmonary circulation

loop provide an exception to this rule – these arteries carry deoxygenated blood from

the heart to the lungs to be oxygenated.

Arteries face high levels of blood pressure as they carry blood being pushed from the

heart under great force. To withstand this pressure, the walls of the arteries are thicker,

more elastic, and more muscular than those of other vessels. The largest arteries of the

body contain a high percentage of elastic tissue that allows them to stretch and

accommodate the pressure of the heart.

Smaller arteries are more muscular in the structure of their walls. The smooth muscles

of the arterial walls of these smaller arteries contract or expand to regulate the flow of

blood through their lumen. In this way, the body controls how much blood flows to

different parts of the body under varying circumstances. The regulation of blood flow

also affects blood pressure, as smaller arteries give blood less area to flow through and

therefore increases the pressure of the blood on arterial walls.

Arterioles are narrower arteries that branch off from the ends of arteries and carry blood

to capillaries. They face much lower blood pressures than arteries due to their greater

number, decreased blood volume, and distance from the direct pressure of the heart.

Thus arteriole walls are much thinner than those of arteries. Arterioles, like arteries, are

able to use smooth muscle to control their aperture and regulate blood flow and blood

pressure.

Capillaries: Capillaries are the smallest and thinnest of the blood vessels in the body

and also the most common. They can be found running throughout almost every tissue

of the body and border the edges of the body’s avascular tissues. Capillaries connect to

arterioles on one end and venules on the other.

Capillaries carry blood very close to the cells of the tissues of the body in order to

exchange gases, nutrients, and waste products. The walls of capillaries consist of only a

thin layer of endothelium so that there is the minimum amount of structure possible

between the blood and the tissues. The endothelium acts as a filter to keep blood cells

inside of the vessels while allowing liquids, dissolved gases, and other chemicals to

diffuse along their concentration gradients into or out of tissues.

Precapillary sphincters are bands of smooth muscle found at the arteriole ends of

capillaries. These sphincters regulate blood flow into the capillaries. Since there is a

limited supply of blood, and not all tissues have the same energy and oxygen

requirements, the precapillary sphincters reduce blood flow to inactive tissues and allow

free flow into active tissues.

Veins and Venules: Veins are the large return vessels of the body and act as the blood

return counterparts of arteries. Because the arteries, arterioles, and capillaries absorb

most of the force of the heart’s contractions, veins and venules are subjected to very

low blood pressures. This lack of pressure allows the walls of veins to be much thinner,

less elastic, and less muscular than the walls of arteries.

Veins rely on gravity, inertia, and the force of skeletal muscle contractions to help push

blood back to the heart. To facilitate the movement of blood, some veins contain many

one-way valves that prevent blood from flowing away from the heart. As skeletal

muscles in the body contract, they squeeze nearby veins and push blood through

valves closer to the heart.

When the muscle relaxes, the valve traps the blood until another contraction pushes the

blood closer to the heart. Venules are similar to arterioles as they are small vessels that

connect capillaries, but unlike arterioles, venules connect to veins instead of arteries.

Venules pick up blood from many capillaries and deposit it into larger veins for transport

back to the heart.

Coronary Circulation 

The heart has its own set of blood vessels that provide the myocardium with the oxygen

and nutrients necessary to pump blood throughout the body. The left and right coronary

arteries branch off from the aorta and provide blood to the left and right sides of the

heart. The coronary sinus is a vein on the posterior side of the heart that returns

deoxygenated blood from the myocardium to the vena cava.

Hepatic Portal Circulation

The veins of the stomach and intestines perform a unique function: instead of carrying

blood directly back to the heart, they carry blood to the liver through the hepatic

portal vein. Blood leaving the digestive organs is rich in nutrients and other chemicals

absorbed from food. The liver removes toxins, stores sugars, and processes the

products of digestion before they reach the other body tissues. Blood from the liver then

returns to the heart through the inferior vena cava.

Blood

The average human body contains about 4 to 5 liters of blood. As a liquid connective

tissue, it transports many substances through the body and helps to maintain

homeostasis of nutrients, wastes, and gases. Blood is made up of red blood cells, white

blood cells, platelets, and liquid plasma.

Red Blood Cells: Red blood cells, also known as erythrocytes, are by far the most

common type of blood cell and make up about 45% of blood volume. Erythrocytes are

produced inside of red bone marrow from stem cells at the astonishing rate of about 2

million cells every second. The shape of erythrocytes is biconcave—disks with a

concave curve on both sides of the disk so that the center of an erythrocyte is its

thinnest part. The unique shape of erythrocytes gives these cells a high surface area to

volume ratio and allows them to fold to fit into thin capillaries. Immature erythrocytes

have a nucleus that is ejected from the cell when it reaches maturity to provide it with its

unique shape and flexibility. The lack of a nucleus means that red blood cells contain no

DNA and are not able to repair themselves once damaged.

Erythrocytes transport oxygen in the blood through the red pigment hemoglobin.

Hemoglobin contains iron and proteins joined to greatly increase the oxygen carrying

capacity of erythrocytes. The high surface area to volume ratio of erythrocytes allows

oxygen to be easily transferred into the cell in the lungs and out of the cell in the

capillaries of the systemic tissues. 

White Blood Cells: White blood cells, also known as leukocytes, make up a very small

percentage of the total number of cells in the bloodstream, but have important functions

in the body’s immune system. There are two major classes of white blood cells:

granular leukocytes and agranular leukocytes.

Granular Leukocytes: The three types of granular leukocytes are neutrophils,

eosinophils, and basophils. Each type of granular leukocyte is classified by the

presence of chemical-filled vesicles in their cytoplasm that give them their function.

Neutrophils contain digestive enzymes that neutralize bacteria that invade the body.

Eosinophils contain digestive enzymes specialized for digesting viruses that have been

bound to by antibodies in the blood. Basophils release histamine to intensify allergic

reactions and help protect the body from parasites.

Agranular Leukocytes: The two major classes of agranular leukocytes are lymphocytes

and monocytes. Lymphocytes include T cells and natural killer cells that fight off viral

infections and B cells that produce antibodies against infections by pathogens.

Monocytes develop into cells called macrophages that engulf and ingest pathogens and

the dead cells from wounds or infections. 

Platelets : Also known as thrombocytes, platelets are small cell fragments responsible

for the clotting of blood and the formation of scabs. Platelets form in the red bone

marrow from large megakaryocyte cells that periodically rupture and release thousands

of pieces of membrane that become the platelets. Platelets do not contain a nucleus

and only survive in the body for up to a week before macrophages capture and digest

them. 

Plasma: Plasma is the non-cellular or liquid portion of the blood that makes up about

55% of the blood’s volume. Plasma is a mixture of water, proteins, and dissolved

substances. Around 90% of plasma is made of water, although the exact percentage

varies depending upon the hydration levels of the individual. Theproteins within plasma

include antibodies and albumins. Antibodies are part of the immune system and bind to

antigens on the surface of pathogens that infect the body. Albumins help maintain the

body’s osmotic balance by providing an isotonic solution for the cells of the body. Many

different substances can be found dissolved in the plasma, including glucose, oxygen,

carbon dioxide, electrolytes, nutrients, and cellular waste products. The plasma

functions as a transportation medium for these substances as they move throughout the

body.

Cardiovascular System Physiology

Functions of the Cardiovascular System 

The cardiovascular system has three major functions: transportation of materials,

protection from pathogens, and regulation of the body’s homeostasis.

Transportation: The cardiovascular system transports blood to almost all of the body’s

tissues. The blood delivers essential nutrients and oxygen and removes wastes and

carbon dioxide to be processed or removed from the body. Hormones are transported

throughout the body via the blood’s liquid plasma.

Protection: The cardiovascular system protects the body through its white blood cells.

White blood cells clean up cellular debris and fight pathogens that have entered the

body. Platelets and red blood cells form scabs to seal wounds and prevent pathogens

from entering the body and liquids from leaking out. Blood also carries antibodies that

provide specific immunity to pathogens that the body has previously been exposed to or

has been vaccinated against.

Regulation: The cardiovascular system is instrumental in the body’s ability to maintain

homeostatic control of several internal conditions. Blood vessels help maintain a stable

body temperature by controlling the blood flow to the surface of the skin. Blood vessels

near the skin’s surface open during times of overheating to allow hot blood to dump its

heat into the body’s surroundings. In the case of hypothermia, these blood vessels

constrict to keep blood flowing only to vital organs in the body’s core. Blood also helps

balance the body’s pH due to the presence of bicarbonate ions, which act as a buffer

solution. Finally, the albumins in blood plasma help to balance the osmotic

concentration of the body’s cells by maintaining an isotonic environment.

The Circulatory Pump 

The heart is a four-chambered “double pump,” where each side (left and right) operates

as a separate pump. The left and right sides of the heart are separated by a muscular

wall of tissue known as the septum of the heart. The right side of the heart receives

deoxygenated blood from the systemic veins and pumps it to the lungs for oxygenation.

The left side of the heart receives oxygenated blood from the lungs and pumps it

through the systemic arteries to the tissues of the body. Each heartbeat results in the

simultaneous pumping of both sides of the heart, making the heart a very efficient

pump.

Regulation of Blood Pressure 

Several functions of the cardiovascular system can control blood pressure. Certain

hormones along with autonomic nerve signals from the brain affect the rate and strength

of heart contractions. Greater contractile force and heart rate lead to an increase in

blood pressure. Blood vessels can also affect blood pressure. Vasoconstriction

decreases the diameter of an artery by contracting the smooth muscle in the arterial

wall. The sympathetic (fight or flight) division of the autonomic nervous system causes

vasoconstriction, which leads to increases in blood pressure and decreases in blood

flow in the constricted region. Vasodilation is the expansion of an artery as the smooth

muscle in the arterial wall relaxes after the fight-or-flight response wears off or under the

effect of certain hormones or chemicals in the blood. The volume of blood in the body

also affects blood pressure. A higher volume of blood in the body raises blood pressure

by increasing the amount of blood pumped by each heartbeat. Thicker, more viscous

blood from clotting disorders can also raise blood pressure.

Hemostasis

Hemostasis, or the clotting of blood and formation of scabs, is managed by the platelets

of the blood. Platelets normally remain inactive in the blood until they reach damaged

tissue or leak out of the blood vessels through a wound. Once active, platelets change

into a spiny ball shape and become very sticky in order to latch on to damaged tissues.

Platelets next release chemical clotting factors and begin to produce the protein fibrin to

act as structure for the blood clot. Platelets also begin sticking together to form a

platelet plug. The platelet plug will serve as a temporary seal to keep blood in the vessel

and foreign material out of the vessel until the cells of the blood vessel can repair the

damage to the vessel wall.

Author

Praveen Buddiga, MD  Physician, Allergy, Asthma and Immunology, Baz Allergy, Asthma and Sinus Center, Fresno, California 

Praveen Buddiga, MD, is a member of the following medical societies: American Academy of Allergy Asthma and Immunology and American College of Allergy, Asthma and Immunology

Disclosure: Meda Honoraria Speaking and teaching; Teva Honoraria Speaking and teaching; AstraZeneca Honoraria Speaking and teaching

Coauthor(s)

Archana Bangalore  Research Coordinator and Volunteer, Alta Family Health Clinic; Volunteer, Fresno Women's Care 

Disclosure: Nothing to disclose.

Chief Editor

Thomas R Gest, PhD  Professor of Anatomy, Department of Pathology and Cell Biology, University of South Florida College of Medicine 

Disclosure: Lippincott Williams & Wilkins Royalty Other