Part 2

Endocrine System

Thyroid Gland

Saddle bag shaped gland

Largest endocrine gland in the body

3 hormones Throxin

Triiodothyronine

Calcitonin

Thyroid hormone

Copyright © 2010 Pearson Education, Inc. Figure 16.1

Pineal gland

Hypothalamus

Pituitary gland

Parathyroid glands

(on dorsal aspect

of thyroid gland)

Thymus

Thyroid gland

Adrenal glands

Pancreas

Ovary (female)

Testis (male)

Figure 16.8

Thyroid Hormone (TH)

Actually two related compounds

T4 (thyroxin)

2 tyrosine molecules + 4 bound iodine atoms

T3 (triiodothyronine)

2 tyrosines + 3 bound iodine atoms

Thyroid Hormone (TH)

1) Iodide enters body

2) Converted to iodine by thyroid gland

3) Iodine binds to thyroglobulin

4) Tyrosine added to iodized thyroglobulin, combined in vacuole

with lysosomes

5) Thyroglobulin freed and recycled while T3/T4 diffuses into

blood

6) T3/T4 bind to thyroxin-binding globulin in blood

7) At tissue receptor T4 converted to active T3 by tissue enzymes

Figure 16.9

To peripheral tissues

T3

T3

T3

T4

T4

Lysosome

Tyrosines (part of thyroglobulin

molecule)

T4

DIT (T2)

Iodine

MIT (T1)

Thyro-

globulin

colloid

Iodide (I–)

Rough

ER

Capillary

Colloid

Colloid in

lumen of

follicle

Thyroid follicle cells

Iodinated tyrosines are

linked together to form T3

and T4.

Iodide

is oxidized

to iodine.

Thyroglobulin colloid is

endocytosed and combined

with a lysosome. Lysosomal enzymes cleave

T4 and T3 from thyroglobulin

colloid and hormones diffuse

into bloodstream.

Iodide (I–) is trapped

(actively transported in).

Thyroglobulin is synthesized and

discharged into the follicle lumen.

Iodine is attached to tyrosine

in colloid, forming DIT and MIT.

Golgi

apparatus

1

2

3

4

5

6

7

Thyroid Hormone (TH)

Major metabolic hormone (catabolism)

Regulates tissue growth and development

Increases reactivity of mature nerve cells

Regulates heart rate

Regulates movement of gastrointestinal tract

Copyright © 2010 Pearson Education, Inc. Figure 16.7

Hypothalamus

Anterior pituitary

Thyroid gland

Thyroid

hormones

TSH

TRH

Target cells Stimulates

Inhibits

Imbalances of Thyroid Hormone

Goiter

Cretinism

Myxedema

Graves’ disease

Copyright © 2010 Pearson Education, Inc. Figure 16.10

Calcitonin

Lowers serum calcium

Inhibits bone resorption

Stimulates uptake by the bone matrix

Antagonist to parathyroid hormone (PTH)

Regulated by Ca2+ concentration in the blood

Negative feedback mechanism

Parathyroid Glands

Four tiny glands embedded in the posterior aspect of the thyroid

Parathyroid hormone (PTH)

Most important hormone in Ca2+ homeostasis

Copyright © 2010 Pearson Education, Inc. Figure 16.11

(b)

Capillary

Chief

cells

(secrete

parathyroid

hormone)

Oxyphil

cells

Pharynx

(posterior

aspect)

Thyroid

gland

Parathyroid

glands

Trachea

Esophagus

(a)

Parathyroid Hormone

Functions Stimulates osteoclasts to digest bone matrix

Enhances reabsorption of Ca2+ by the kidneys

Increases absorption of Ca2+ by intestinal mucosa

Negative feedback

Rising Ca2+ in the blood inhibits PTH release

Copyright © 2010 Pearson Education, Inc. Figure 16.12

Intestine

Kidney

Bloodstream

Hypocalcemia (low blood Ca2+) stimulates

parathyroid glands to release PTH.

Rising Ca2+ in

blood inhibits

PTH release.

1 PTH activates

osteoclasts: Ca2+

and PO43S released

into blood.

2 PTH increases

Ca2+ reabsorption

in kidney

tubules.

3 PTH promotes

kidney’s activation of vitamin D,

which increases Ca2+ absorption

from food.

Bone

Ca2+ ions

PTH Molecules

Adrenal Glands

Paired, pyramid-shaped glands atop the kidneys

Essentially two glands in one

Adrenal medulla

Nervous tissue: part of the sympathetic nervous system

NE and Epinephrine

Adrenal cortex

Three layers of glandular tissue

Synthesize and secrete steroid hormones

Figure 16.1

Pineal gland

Hypothalamus

Pituitary gland

Parathyroid glands

(on dorsal aspect

of thyroid gland)

Thymus

Thyroid gland

Adrenal glands

Pancreas

Ovary (female)

Testis (male)

Adrenal Cortex

Three layers that produce corticosteroids

Outer layer = mineralocorticoids

Middle layer = glucocorticoids

Inner layer = sex hormones, or gonadocorticoids

Figure 16.13a

• Cortex

Kidney

• Medulla

Adrenal gland

Capsule

Zona

glomerulosa

Zona

fasciculata

Zona

reticularis

Adrenal

medulla

(a) Drawing of the histology of the

adrenal cortex and a portion of

the adrenal medulla

Me

dulla

C

ortex

Mineralocorticoids

Regulate extracellular Na+ and K+ Na+: affects ECF volume, blood volume, blood pressure

K+: sets resting membrane potential of cells

Aldosterone is most important Stimulates Na+ reabsorption (and water retention) by kidneys

Stimulates K+ secretion

Figure 16.14

Primary regulators Other factors

Blood volume

and/or blood

pressure

Angiotensin II

Blood pressure

and/or blood

volume

K+ in blood

Direct

stimulating

effect Renin

Initiates

cascade

that

produces

Kidney

Hypo-

thalamus

Heart

CRH

Anterior

pituitary

Zona glomerulosa

of adrenal cortex

Enhanced

secretion

of aldosterone

Targets

kidney tubules

Absorption of Na+ and

water; increased K+ excretion

Blood volume

and/or blood pressure

Inhibitory

effect

Stress

ACTH Atrial natriuretic

peptide (ANP)

Secretion mainly

controlled by

blood pressure and

potassium levels

Glucocorticoids

Regulate carbohydrate metabolism

Keep blood sugar levels relatively constant

Gluconeogenesis

Suppress inflammation

Vasoconstriction

Vessel permeability

Stabilizing lysosomes

Imbalances of Glucocorticoids

Cushing’s disease

Addison’s disease Also involves deficits in mineralocorticoids

Figure 16.15

Gonadocorticoids (Sex Hormones)

Most are androgens (male sex hormones)

Converted to testosterone in tissue cells or estrogens in females

Supplement hormones secreted by gonads

May contribute to

Onset of puberty

Secondary sex characteristics

Sex drive

Adrenal Medulla

Epinephrine

Affects the metabolic rate of all cells

Bronchial dilation

Increased blood flow to skeletal muscles and heart

Norepinephrine

Increased blood pressure

Increased heart rate

Increased stroke volume

Figure 16.16

Short-term stress More prolonged stress

Stress

Hypothalamus

CRH (corticotropin-

releasing hormone)

Corticotroph cells

of anterior pituitary

To target in blood

Adrenal cortex

(secretes steroid

hormones)

Glucocorticoids Mineralocorticoids

ACTH

Catecholamines

(epinephrine and

norepinephrine)

Short-term stress response

1. Increased heart rate

2. Increased blood pressure

3. Liver converts glycogen to glucose and releases

glucose to blood

4. Dilation of bronchioles

5. Changes in blood flow patterns leading to decreased

digestive system activity and reduced urine output

6. Increased metabolic rate

Long-term stress response

1. Retention of sodium

and water by kidneys

2. Increased blood volume

and blood pressure

1. Proteins and fats converted

to glucose or broken down

for energy

2. Increased blood glucose

3. Suppression of immune

system

Adrenal medulla

(secretes amino acid-

based hormones)

Preganglionic

sympathetic

fibers

Spinal cord

Nerve impulses

Imbalances in Adrenal Medulla

Adrenal medullary hormones not essential for life

Pheochromocytoma

Pancreas

Long, flat gland near stomach

Exocrine function Produces enzyme-rich juice for digestion

Endocrine function

Pancreatic islets (islets of Langerhans)

Alpha () cells = glucagon

Hyperglycemic hormone

Beta () cells = insulin

Hypoglycemic hormone

Figure 16.1

Pineal gland

Hypothalamus

Pituitary gland

Parathyroid glands

(on dorsal aspect

of thyroid gland)

Thymus

Thyroid gland

Adrenal glands

Pancreas

Ovary (female)

Testis (male)

Glucagon

Major target is the liver Release of glucose to the blood

Hyperglycemic factor

Insulin

Effects Lowers blood glucose levels

Enhances membrane transport of glucose

Inhibits glycogenolysis and gluconeogenesis

Figure 16.18

Liver

Liver

Tissue cells

Stimulates glucose uptake by cells

Stimulates

glycogen

formation Pancreas

Pancreas

Insulin

Blood

glucose

falls to

normal

range.

Stimulates

glycogen

breakdown

Blood

glucose

rises to

normal

range.

Glucagon

Stimulus

Blood

glucose level

Stimulus

Blood

glucose level

Glycogen Glucose

Glycogen Glucose

Imbalances of Insulin

Diabetes mellitus (DM) Due to hyposecretion or hypoactivity of insulin

Vascular component

Three cardinal signs of DM Polyuria = copious urine output

Polydipsia = excessive thirst

Polyphagia = excessive hunger and food consumption

Table 16.4

Diabetes Mellitus

Type I

Type II

Gestational

Insulin cont.

Other hormones affecting insulin levels

Growth hormone (GH)

Adrenocorticotropic hormone (ACTH)

Minor Endocrine Glands

Thymus

Pineal gland

Thymus

2 lobed organ high in chest

Thymosins = lymphocytes

Active during fetal development and for first two

years after birth

Pineal Gland

Small gland hanging from the roof of the third ventricle

Melatonin

Timing of sexual maturation and puberty

Photoperios

Physiological processes that show rhythmic variations

Body temperature, sleep, appetite

Not well understood in humans

Stress

Physical

Psychological

Strong emotional reactions

Individual reactions vary

The Stress Response

Changes largely mediated by hypothalamus

Three stages Alarm (acute, sympathetic)

Resistance (chronic, endocrine)

Exhaustion

Temporary change in homeostasis =

General Adaptation Syndrome (GAS)

Alarm Reaction

Immediate Hypothalamus

Sympathetic nervous system

Adrenal medulla

Increased serum glucose

Increased circulation

Resistance Reaction

Long-term modification Hypothalamus

Pituitary gland

Many effects… Increases energy availability

Produces new proteins

Improves circulation

Figure 16.16

Short-term stress More prolonged stress

Stress

Hypothalamus

CRH (corticotropin-

releasing hormone)

Corticotroph cells

of anterior pituitary

To target in blood

Adrenal cortex

(secretes steroid

hormones)

Glucocorticoids Mineralocorticoids

ACTH

Catecholamines

(epinephrine and

norepinephrine)

Short-term stress response

1. Increased heart rate

2. Increased blood pressure

3. Liver converts glycogen to glucose and releases

glucose to blood

4. Dilation of bronchioles

5. Changes in blood flow patterns leading to decreased

digestive system activity and reduced urine output

6. Increased metabolic rate

Long-term stress response

1. Retention of sodium

and water by kidneys

2. Increased blood volume

and blood pressure

1. Proteins and fats converted

to glucose or broken down

for energy

2. Increased blood glucose

3. Suppression of immune

system

Adrenal medulla

(secretes amino acid-

based hormones)

Preganglionic

sympathetic

fibers

Spinal cord

Nerve impulses Fight or Flight Resistance

Exhaustion

Stressor too strong K+ loss = cell death

Glucocorticoid depletion = cell starvation

Immune system failure

General Adaptation Syndrome

(or Stress Response)

Questions?