Anatomy and Physiology II
Chapter 16: Endocrine System
I. Intro:
A. Endocrinology = Study of chemical means (hormones) of communication within body.
- e.g. growth, metabolism, sex characteristics & even personality
B.
Nervous
Endocrine
Fast-acting
Slow acting
Short lasting
Long acting
Electrical transmission
Chemical transmission
C. Hormone= Chemical signal transported by circulatory system causing a response in
a specific “target” cell [each has its own specific shape]
- More than 50 types of human hormones
D. 3 types:
a. Amino acid - based
- (most common) e.g. thyroxine; epinephrine
b. Steroids
- made from cholesterol
- e.g. gonadol; adrenocortical
c. Eicosanoids = active lipids
- e.g. prostaglandins
- increase B.P.
- increase uterine contractions
- increase blood clotting
- pain
E. Hormones act in opposition to each other
e.g. Insulin -- Decreases blood sugar
Glucagon -- Increases blood sugar
F. Pheromones = Chemicals that function in communication Between animals
e.g. Ants:
- War
- Alarm
- Food recruitment
- Detect low concentrations
II. General Mechanism of Hormone Action
A. Hormones “alter” target cell activity
a. Increase or Decrease enzyme activity
b. Increase mitosis
c. Changes membrane permeability
d. Increase synthesis proteins/secretion
B. Target Cell Specificity= “specific fit”
Depends on:
1. Blood levels of hormones
2. # of Receptors
3. Affinity between receptor & hormone
** Down-Regulation** = Prolonged exposure to hormones desensitizes target cells
e.g. Diabetes Type II
** Up-Regulation** = Target cells make more receptors in response to increases
hormone levels
e.g. Estrogen causes uterine receptors to uptake progesterone
C. Hormone Interactions
a. Permissiveness = one hormone needs another to be present
e.g. Thyroxine “permits” reproductive hormones for development
b. Synergism = one hormone enhances effects of another
e.g. epinephrine & glucagon - together cause liver to release glucose.
c. Antagonism = one hormone opposes action of another
e.g. Insulin - decreases blood glucose
glucagon - increases blood glucose
III. Types of Hormone Mechanisms
A. Steroid Hormones - Pass through cell membrane & enters nucleus ---> directly
causes transcription of certain genes
e.g. estrogen; progesterone
B. Peptide Hormones
* Cant Pass thru cell membrane.
Instead: a. Cyclic AMP SYSTEM
1. Bind to receptors (1st degree messenger) on cell mem.
2. Binding causes G-Protein (2nd degree messenger) to be activated using
MTP
3. Active G-Protein causes Adenylate cyclase to be activated
4. Adenylate Cyclase makes ATP -----> cAMP
5. cAMP activates Protein Kinases which phosphorylate proteins (this is the
response of target cells)
b. Inositol Triphosphate (IP3) System:
e.g. Neurotransmitters + Growth hormone + AD/+ Oxytocin
1. Hormone-receptor bind
2. Activated G-Protein
3. Membrane enzyme cleaves (PIP2) phospholipid into:
IP3
Diacylglycerol
Causes release of Ca++from E.R.
Activates protein Kinases
Changing enzyme activity
IV. Major Endocrine Organs
A. Hypothalamus “master gland”
a. part of lower brain that receives info from other parts of the body
b. Anatomy - neurosecretory cells:release hormones to pituitary when stimulated by
nerve cells
c. connected to posterior pituitary via hypothalmic-hypophsyeal tract
B. Pituitary Gland = obeys orders from hypothalamus
a. Posterior Lobea. Made of axons of hypothalmic neurons
b. Stores: ADH (antidiuretic hormone)
- H2O conserving, alcohol
- Oxytocin - Uterine contractions
- made by hypothalamus
- mechanism: IP3 System
b. Anterior Lobe
Releases 4 tropic hormones <---- stimulate other glands (releasing hormone)
- Mechanism: cAMP system
a. TSH (Thyroid Stimulating Hormone)
- Acts on thyroid to make thyroxine
b. Adrenocorticotropin (ACTH)
- acts on adrenal cortex to make corticosteroid hormones (e.g.
hypoglycemia)
c. Gonadotropin
- Stimulated by GnRH (gonadotropin releasing hormones) made by
hypothalamus
- LH (luteinizing hormone)
- promotes gamete development
- promotes gonadal hormone production
- ovulation
- FSH (Follicle Stimulating hormone)
- Development of gametes
d. Prolactin
- milk production in breasts
e. Growth Hormone
- stimulates bones [epiphyseal plate closes at night] & skeletal muscles to
increase size & divide
- Giantism (8' tall)
- Acromegaly (GH continues after epiphyseal plate closing)
- Dwarfism (4' tall)
C. Thyroid Gland
a. Anatomy
- Largest endocrine gland
b. Triiodothyronine & Thyroxine
(T3)
(T4)
I
I
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V
c. Physiology = regulates metabolism
* Hyperthyroidism - overactive thyroid
a. overactive cells
b. excessive TSH
- Graves Disease - autoimmune ( antibodies mimic TSH) --->
overstimulates thyroid
* Hypothyroidism - under active thyroid
- cretinism (infants) replacement therapy
- goiter = enlarged thyroid b/c not enough celld
- Symptoms weigh gain, intolerance to cold, increased cholesterol
* control of hormone production by negative feedback
d. Calcitonin - lowers blood Ca++
- made by parafollicular cells
- antagonist to PTH
- most important in childhood
D. Parathyroid Gland
a. Embedded within thyroid
b. Homeostasis of calcium
* if thyroid is totally removed, (why do some people still regulate calcium? b/c
parathyroid may also be in chest or neck)
c. Chief cells secrete PTH (parathyroid hormone)
Increase blood calcium
a. causes release of calcium from bone (osteoclasts)
b. Causes reabsorption of Ca++ from kidneys (intestinal mucosal cells).
d. PTH activated Vitamin D (ingested)
I
V
Calcitriol (active)
E. Adrenal (suprarenal) Glands - atop kidneys
“above Kidney”
a. Adrenal Cortex
a.
bulk of gland; under pituitary control (slow response)
b.
makes steroid hormones (Corticosteroids)
Mineralocorticoids
Gonadocorticoids
Glucocorticoids
mineral and water balance
made by zona reticularis
metabolic hormones
e.g. aldosterone
(osmoregulation) (95%
made)
weak female sex
hormones
^ glucose availability
^ water in blood
female sex drive
zona fasiculata
zona glomerulosa
b. Adrenal Medulla
a.
“knot of nervous tissue”
b.
involved in sympathetic N.S.
a. Secretes epinephrine (adrenaline)(heart rate) & norepinephrine
(noradrenaline)(peripheral BP)
Cause: Short term
“fight or flight response”
^ HR, Stroke volume
^ blood supply to heart, skeletal muscles
decrease blood to internal organs
^ available energy (use of glucose by liver & muscles)
b. Sympathetic Nervous System
- stimulates adrenal medulla by releasing acetylcholine
* Cushing's Syndrome - Hypersecretion (adrenal tumor) of glucocorticoids
1. buffalo hump
2. facial edema
3. fractures; muscle atrophy
* Addison's Disease - hyposecretion of adrenal cortex
a. weight loss
b. hypotension
c. decreased Na+ Increased K+
d. Dehydration
F. Pancreas (endocrine + exocrine)
- Contains clusters of endocrine cells called Islets of Langerhans
1. Each islet has:
a. Alpha Cells - Secrete glucagon
b. Beta Cells - Secrete insulin
* insulin + glucagon are antagonistic
2. Blood sugar set point = 90 mg/ml
a. when sugar level is too high, insulin lowers it.
b. when sugar level is too low, glucagon increases it.
3. Diabetes Mellitus
Insulin - low, not effective
- Starvation
- Ketonuria - fat metabolize
- decreased pH
- Polyuria - urination
- Polydipsia - thirst
- Polyphagia - hunger
i. Type I - Diabetes
- autoimmune attack
- attack on pancreas
ii. Type II - Diabetes
- Insulin Deficiency
- down regulation
G. Gonads Testes
Androgens e.g.
testosterone
Ovaries
Estrogens
H. Pineal Gland - (in brain)
- produces melatonin which causes sleepiness
- in darkness (esp. winter) more melatonin makes you more tired
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