THE ENDOCRINE SYSTEM HTTP://WWW.YOUTUBE.COM/WATCH?V=WVRLHH14Q3O

Chapter 10

THE ENDOCRINE SYSTEM Contributes to:

control of growth, development, reproduction, behaviour, energy metabolism, and water balance

By: Secreting hormones

To control Organ and tissue

functions

ENDOCRINE SYSTEM A system of ductless

secretory organs (glands) located in various parts of the body

Include Pineal, anterior/posterior

pituitary, thyroid, parathyroid, thymus, adrenal, islets of Langerhans, ovaries, testes, mammary

Main function Secrete hormones directly into

the blood or extracellular fluid

HYPOTHALAMUS Is not a gland but a region of the brain Part of the nervous system Very important for function of endocrine system Produce neurohormones that stimulate or

inhibit production of other hormones in the pituitary gland

HORMONES OF THE HYPOTHALAMUS Thyrotropin-releasing hormone (TRH)

Stimulates release of thyroid-stimulating hormone (TSH) Gonadotropin-releasing hormone (GnRH)

Stimulates release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH)

Growth hormone-releasing hormone (GHRH) Stimulates release of growth hormone (GH)

Corticotropin-releasing hormone (CRH) Release of adrenocorticotropic hormone (ACTH)

Somatosin Inhibits the release of growth hormone (GH)

Dopamine Inhibits the release of thyroid-stimulating hormone (TSH)

HORMONES: MAINTAINING HOMEOSTASIS

Chemical management system for the body Chemicals produced by cells in one part of the body

the regulate the processes of cells in another part of the body

Chemical messengers – act on cells from another part of the body

Local regulators – act on nearby cells Self regulators – cells that produce chemicals to

stimulate their own cellular processes

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HORMONES Produced and secreted by

cells, tissues and organs that compose the endocrine system (glands) directly into the blood or extracellular fluid

Hormones are circulated throughout the body

Only target cells will respond to specific hormones

Hormones are broken down by enzymes in target cell, liver or kidneys where they are reused or excreted

HORMONES Secreted in an inactive form –

prohormones Prohormones are converted by target

cells or by enzymes in the blood to an active form

Angiotensinogen → angiotensin

HORMONES Protein hormones

Consist of AA – 3 to 200 in length

Usually hydrophilic – water soluble

Diffuse well through blood Steroid hormones

Derived from cholesterol Not water soluble Usually encased with protein

to travel through blood Pass easily through lipid

bilayer

HORMONE MECHANISMS Water-Soluble

Cannot pass membrane Bind to receptor molecules in the

cell membrane Signal is activated Secondary messenger is

activated Change is caused inside cell Acts in the cytosol or the nucleus

Glucagon Breakdown of glycogen into

glucose

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HORMONE MECHANISMS Lipid-Soluble

Can pass membrane (lipid) Bind to receptors inside a cell

(cytosol or nucleus) Turn on or off an action of a

specific gene Changes amount of protein

that is synthesized by cell Aldosterone

Increase sodium absorption → increases water retention → increase blood pressure

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MAJOR FEATURES OF HORMONE MECHANISMS Only the cells that contain surface or internal

receptors for the hormones respond to the hormones

Once bound to their receptors, hormones produce a response by turning cellular processes on or off. They do this by altering the proteins that are functioning in or produced by the cell

Hormones are effective in very small concentrations because of the amplification that occurs in both the surface and internal receptor mechanisms

The response to a hormone differs among target organs and among species

HORMONES: NEGATIVE FEEDBACK MECHANISMS

Secretion of hormones are regulated by negative feedback mechanisms

Hormones inhibit other hormones Multiple hormones can be secreted at a

time

THE PITUITARY GLAND The Master Gland

Produces hormones that control most of the other endocrine glands

THE PITUITARY GLAND Made up of anterior lobe

and posterior lobe Links endocrine system

to nervous system via portal vein (hypothalamus)

Influenced by hypothalamus Releasing

hormones/inhibiting hormones

2. portal vein4. anterior

pituitary gland5. hypophyseal

vein6. posterior

pituitary gland8. pituitary stalk9. capillary

network10. neurons11. neurosecretory

cells12. hypothalamus

ANTERIOR PITUITARY GLAND Secretes 6 major hormones

into the bloodstream which influence hormone secretion in other glands Prolactin, growth hormone,

thyroid-stimulating hormone, adrenocorticotropic hormone, follicle-stimulating hormone, luteinizing hormone

Other hormones produced Melanocyte-stimulating

hormone, endorphins

PROLACTIN

GROWTH HORMONE Cell division, protein

synthesis, bone growth IGF – insulin growth

factor that stimulates these functions

Also Conversion of glycogen to

glucose, fats to fatty acids – regulates levels in blood

Stimulates cells to take up FA, AA and limits muscle cells to take up glucose

GROWTH HORMONE Underproduction – dwarfism Overproduction – gigantism

THYROID-STIMULATING HORMONE

ADRENOCORTICOTROPIC HORMONE

FOLLICLE-STIMULATING HORMONE/LUTEINIZING HORMONE

MELANOCYTE-STIMULATING HORMONE Causes darkening in humans causing

the release of melanin in the skin and hair

Protects from UV rays

ENDORPHINS Natural pain killers

POSTERIOR PITUITARY GLAND Stores and releases

2 major hormones into the bloodstream Antidiuretic hormone

(vasopressin), oxytocin

These hormones are produced by the hypothalamus and stored here

ANTIDIURETIC HORMONE (VASOPRESSIN)

Causes distal convoluted tubule to become permeable to water

Helps maintain water balance

OXYTOCIN

THYROID GLAND Located in the front

of the throat and shaped like a bow tie

Secretes thyroxine (T₄),

triiodothyronine, calcitonin

THYROXINE (T₄) Contains 4 iodine

atoms When iodine levels

are low thyroid will continue to grow resulting in a goiter

CALCITONIN Protein hormone that lowers levels of

Ca²⁺ in blood

PARATHYROID GLAND 4 spherical glands (size of a pea) located

on each side of the posterior surface of the thyroid gland

Secretes Parathyroid hormone

PARATHYROID HORMONE Stimulates enzymes in kidneys to convert

vitamin D into calcitrol increasing absorption of Ca²⁺ and phosphates from food

Underproduction Muscle cramps Osteoporosis

Overproduction Kidney stones

ADRENAL GLANDS Consist of two regions

Adrenal medulla – contains highly modified neuro-secretory neurons

Adrenal cortex – contains non-neural endocrine cells

ADRENAL MEDULLA Secretes

Epinephrine, norepinephrine These chemicals can act as hormones or

neurotransmitters (transmit nerve signals)

Part of the “fight or flight” response

EPINEPHRINE/NOREPINEPHRINE Released when body encounters stresses Epinephrine

Increase heart rate glycogen and fat breakdown Skeletal muscles, lungs blood vessels dilate

increasing blood flow Blood vessels everywhere else constrict Blood pressure raises Reduces water loss Digestive system slows Used to counter anaphylaxis

ADRENAL CORTEX Secretes

Aldosterone, cortisol

PINEAL GLAND Located near the centre of the

brain Regulates several biological

rhythms Photoreceptors in the eyes

influence pineal gland – light inhibits melatonin secretion

Helps to synchronize biological clock

Secretes melatonin

REGULATING BLOOD SUGAR Occurs automatically in

our body Pancreas – contain both

exocrine/endocrine glands

Exocrine secretes digestive

enzymes into the small intestine

Endocrine Islets of Langerhans -

Secretes insulin (beta cells) and glucagon (alpha cells)

INSULIN/GLUCAGON Regulate the ability of most tissues in

the body to metabolize fuel substances (glucose, fats, proteins)

INSULIN Secreted by beta cells Lower blood glucose levels by

Acts on skeletal muscles, liver cells, adipose tissue (fat) to uptake glucose

In the Liver Lowers fatty acid levels promotes fatty acid uptake and

storage in adipose tissue Inhibits breakdown of fats into fatty

acids Lowers amino acid levels Promotes protein synthesis Inhibits breakdown of proteins

GLUCAGON Secreted by alpha cells Increase blood glucose

levels by Stimulating breakdown of

glycogen into glucose Stimulates breakdown of fats

into fatty acids Stimulates breakdown of

proteins into amino acids Stimulate cells to use amino

acids and non-carbohydrates to synthesize glucose

GLUCOCORTICOIDS Cortisol – Helps raise

blood glucose levels using three mechanisms Stimulate synthesis of

glucose from fats and proteins

Reduce glucose uptake by the body cells except in the central nervous system

Promote breakdown of fats and proteins into fatty acids and amino acids as alternative fuels

GLUCOSE LEVELS THROUGHOUT THE DAY

UNSTABLE LEVELS OF GLUCOSE Hyperglycemia (above 200mg/dL of blood)

Blood glucose levels are too high (norm 115-200mg/dL)

Symptoms Frequent urination, sugar in the urine, vision

problems, fatigue, weight loss Hypoglycemia (below 70mg/dL of blood)

Blood glucose levels are too low (norm 70-115mg/dL)

Symptoms Nervousness, cold sweats, hunger, headaches,

weakness

DIABETES High glucose levels in the blood caused

by problems with insulin production Symptoms

Frequent urination, increased thirst, increased appetite

Classified into three different types Type 1 Type 2 Gestational

TYPE 1 Also called juvenile diabetes or insulin-

dependant Beta cells do not produce any insulin Daily administration of insulin is required

usually by injection or pump

TYPE 2 Reduced insulin production

or the inability of insulin to bind to its receptors properly

Developed in adulthood and is associated with obesity

90% of diabetics have this type

Controlling diet and exercise helps restore normal levels of insulin production

GESTATIONAL Occurs in about 2 to

10% of pregnant women

High blood glucose levels develop during pregnancy

Usually a temporary condition but does increase the risk of both mother and child developing later in life

REPRODUCTIVE HORMONES

Gonads – sex glands Males – testes Females – ovaries

Sex hormones Androgens, estrogens,

progestins Regulate development

of male and female

reproductive systems, sexual characteristics, mating behaviour

http://www.youtube.com/watch?v=_7rsH2loIY8

FEMALE REPRODUCTIVE SYSTEM Pair of ovaries

Located in abdominal cavity Produce female gametes

(ova, eggs) Produce estrogen and

progesterone FSH and LH from the

pituitary gland stimulate the maturation of the follicles in the ovary and trigger ovulation

ESTROGEN Estradiol

Stimulates maturation of the sex organs at puberty

Development of secondary sexual characteristics – breast development, body hair, widening of pelvis

Sex drive

PROGESTINS Progesterone

Maintains uterus for implantation of a fertilized egg

Growth and development of an embryo

OOGENESIS Production and release of

eggs (ova) by the ovaries Releases oocytes -

immature eggs that have undergone 1 meiotic division

Polar body is associated with it Disintegrates quickly

Females produce up to 1 million

Only ~380 are ovulated before menopause

OVULATION Monthly release of one or a few

developing oocytes into the oviduct

Burst of LH causes follicle to rupture

Ova becomes ovum Moves through the oviduct

(fallopian tubes) via cilia that line these tubes

Fertilization occurs here in the oviduct

undergoes second meiotic division only if penetrated by sperm cell producing a zygote

If not fertilized egg will degenerate

OVARIAN CYCLE Occurs from puberty to menopause Involves release of a mature egg approx

every 28 days Coordinated with the menstrual cycle

(month) Prepares the uterus to implant the egg if

fertilization occurs

CORPUS LUTEUM LH causes ruptured follicle to grow into an

enlarged yellowish structure Initiates luteal phase – prepares uterus to

receive an egg If egg is fertilized: Acts as an endocrine gland- secretes estrogens,

progesterone and inhibin Progesterone – inhibits GnRH – FSH LH Inhibin prevents secretion of FSH If egg is not fertilized Corpus luteum shrinks

MENSTRUAL CYCLE Begins at day 0 Results from the breakdown of the endometrium Releases blood and tissue breakdown products from

the uterus to the outside through the vagina Day 4 or 5 – flow ceases and endometrium begins

to grow again Same hormones that control ovarian cycle control

this cycle

MENOPAUSE High levels of sex

hormones stops Late 40’s or early 50’s Menstrual/Ovarian

cycle stops Side effects

Hot flashes, headaches, mood swings

Treated with HRT (hormone replacement therapy)

MALE REPRODUCTIVE SYSTEM Testes

Affect the development of male secondary characteristics

Secrete androgens (testosterone)

Stimulates puberty, facial hair, vocal cords, sex drive

Spermatogenesis – production of sperm

Release of testosterone in the body is controlled by LH which is controlled by GnRH

SPERMATOGENESIS

Sperm development from spermatogonia Takes about 9 to 10 weeks -

spermatogonium to sperm Testes produce about 130 million fertile

sperm each day

SPERMATOGENESIS Leydig cells - secrete

testosterone Sertoli cells – supply

nutrients to spermatocytes and seal them off from body’s blood supply

Coiled seminiferous tubules located in epididymis store mature sperm

Vas deferens – transport sperm upon ejaculation