Chapter 2: The Endocrine System

Question 1

Endocrine system

Answer 1

Consists of endocrine glands which have cells that release chemical messages (i.e. hormones) into the blood stream

Question 2

Endocrine
Autocrine
Paracrine

Answer 2

Not mutually exclusive.

Question 3

Autocrine

Answer 3

Pertaining to a signal secreted by a cell into the environment that affects the transmitting cell.

Question 4

Endocrine gland

Answer 4

A ductless gland from which hormones are released into the blood system in response to specific physiological signals.

Question 5

Paracrine

Answer 5

Secretion of locally acting biological substances from cells.

Question 6

General features of the endocrine system

Answer 6

1. Endocrine glands are ductless and secrete hormones directly into the blood.

(Exocrine glands DON’T have ducts/tubes).
Some endocrine glands are not entirely glandular in nature.

2. Secreted into the blood stream
3. Rich blood supply
4. Can travel in the blood to virtually every cell in the body
5. Hormone receptors (lock) are specific binding sites that interact with a particular hormones of class of hormones (key)

Question 7

PINEAL GLAND

Answer 7

Located within the brain, between the telencephalon and diencephalon

Pinealocytes

Melatonin:
sleep, biological rhythms

Over the course of vertebrate evolution, the primary function of pineal cells has shifted from photoreception to neurosecretion.

Question 8

HYPOTHALAMUS

Answer 8

Part of the brain located below the thalamus

Groups neuronal cell bodies (nuclei)

A variety of vital endocrine, behavioral, and autonomic functions can be localized to particular nuclei of the hypothalamus

In the median eminence, specialized neurons called neurosecretory cells secrete neurohormone (hormones released from a neuron) into the blood vessels of the pituitary

Question 9

HYPOTHALAMUS Inputs

Answer 9

Sensory inputs:
Smell, taste, visual, somatosensory

Blood borne signals:
Sugar, mineral levels, immune products, hormones

Neural inputs:
Hippocampus, amygdala, cortex, brainstem, spinal cord

Hypothalamus:
Detects changes in internal & external environment and responds by changing its output of hormones

Question 10

Hypothalamic Releasing Hormones

Answer 10

Gonadotropin Releasing Hormone (GnRH)

Corticotropin Releasing Hormone (CRH)

Thyrotropin Releasing Hormone (TRH)

Somatocrinin or Growth Hormone Releasing Hormone (GHRH)

Question 11

Hypothalamic Inhibitory Hormones

Answer 11

Somatostatin or GH Inhibiting Hormone (GHIH)

Dopamine (DA) inhibits prolactin secretion from the anterior pituitary

Question 12

Prolactin

Answer 12

A protein hormone that is highly conserved throughout vertebrate evolution and has many physiological functions, which can be broken down into 5 basic classes:

(1) reproduction
(2) growth & development
(3) water and electrolyte balance
(4) maintenance of integumentary structures
(5) actions on steroid-dependent target tissues or synergisms with steroid hormones to affect target tissues.

Prolactin inhibitory hormone (PIH)
Dopamine inhibits prolactin secretion from the anterior pituitary.

Question 13

PITUITARY GLAND

Answer 13

Also called the hypophysis

Pituitary connected to base of hypothalamus by infundibulum (contains axons and blood vessels)

“master gland”

but it is highly regulated..

2 distinct components:
Anterior pituitary (pars anterior or adenohypophysis)
Posterior pituitary (pars nervosa or neurohypophysis)
Have different embryological origins

Hypothalamus communicates with anterior and posterior pituitary differently

Question 14

Posterior pituitary

Answer 14

pars nervosa or neurohypophysis

this section is derived from a downgrowth of neural tissue from the hypothalamus.

The posterior pituitary releases oxytocin (stimulates contraction of uterine muscles; stimulates release of milk by mammary glands) and vasopressin (stimulates increased water reabsorption by kidneys; stimulates constriction of blood vessels).

Hormones are secreted directly from neurons into the blood

Nonapeptides:
The hormones of the posterior pituitary are of peptide class, specifically nonapeptides (they contain 9 amino acids)

Question 15

Anterior pituitary

Answer 15

Adenohypophysis or pars anterior

this part has an embryological origin as an epithelial upgrowth from the foetal oral cavity called Rathke’s Pouch.

The anterior lobe of the pituitary secretes many tropic hormones—including TSH, FSH, LH, ACTH, growth hormone, and prolactin—that travel through the bloodstream and regulate endocrine glands throughout the body.

Receives little if any neural input

Neurohormones from the hypothalamus reach the anterior pituitary via the portal blood system

Causes release of tropic hormones

Question 16

Oxytocin

Answer 16

Posterior Pituitary Hormone

Social, reproductive, and parental behaviors

Uterine contractions during childbirth
Brand Name: Pitocin

Milk let-down reflex

Nonapeptides

Question 17

Tropic hormones

Answer 17

Hormones from the anterior pituitary that stimulate various physiological processes,either by acting directly on target tissues or by causing other endocrine glands to release hormones.

Question 18

Vasopressin

Answer 18

Also known as Antidiuretic Hormone (ADH)

Main target: Kidney, arterioles

Water balance (retention);
Alcohol, urination, and dehydration-related hangover

Blood pressure:
During hemorrhage, ADH acts as a vasoconstrictor to increase blood pressure

Nonapeptide

Question 19

gonadotropins

Answer 19

Luteinizing Hormone (LH)  &
Follicle Stimulating Hormone (FSH) are called gonadotropins because in response to GnRH, LH & FSH stimulate hormone production in the gonads, as well as the development and maturation of gametes (sperm or eggs)

Question 20

Thyroid Stimulating Hormone (TSH)

Answer 20

stimulates thyroid

Question 21

Prolactin (Prl)

Answer 21

In response to TRH, PRL promotes lactation

Question 22

Alcohol is an inhibitor of Vasopressin

Answer 22

….

Question 23

Thyroid gland

Answer 23

H-shaped structure that partially surrounds upper trachea

Consists of many sphere-shaped follicles that produce, store, and secrete thyroid hormones

Unique because it can store a large amount of hormone

Question 24

Thyroid Hormones

Answer 24

2 thyroid hormones released in response to TSH from the anterior pituitary:
Triiodothyronine (T3)
Thyroxine (T4)

Derived from the amino acid tyrosine and require iodine for their production

3 general effects:

1) Alter growth
2) Influence reproduction
3) Affect metabolism

Disorders of the thyroid:
Goiter (Iodine)
Hyperthyroidism
Graves Disease (autoimmune disorder)
Hypothyroidism (common in women who have just given birth)
Hashimoto’s Thyroidosis (autoimmune disorder)
Cretinism

Permissive effects: Always the bridesmaid never the bride
Needs to be there or serious issues occur, but as long as its barely there, its ok
Almost every cell in the body is effected by the thyroid’s hormones

Question 25

Pancreas

Answer 25

Both an endocrine and exocrine gland

Exocrine cells produce and secrete digestive juices into the intestines which breakdown food

Endocrine tissues are embedded in exocrine tissues called Islets of Langerhans – secrete hormones that control blood glucose levels

Question 26

Pancreatic Hormones

Answer 26

Insulin (β cells): lowers blood sugar by promoting the liver to store glycogen

Glucagon (α cells): increases blood sugar by stimulating the breakdown of glycogen in the liver

Somatostatin (δ cells):regulate and fine-tune the insulin and glucagon-producing cells

Question 27

Diabetes

Answer 27

Type 1: body attacks insulin production cells and kills them

Type 2: the body makes insulin, but the cells are rendered insensitive to insulin, and don’t respond

Question 28

Gastrointestinal Tract

Answer 28

Different than other endocrine glands because:

The endocrine tissues of the gastrointestinal tract are scattered through the gut and are NOT located in a single glandular organ

The gastrointestinal hormones regulate the cells and organs in which they are produced

3 major hormones that control various aspects of digestion, stimulating exocrine glands of the gut and pancreas
Gastrin
Secretin
Cholecystokinin (CCK)

Many of these hormones have also been discovered in the brain and affect behaviors, including feeding

Question 29

Ghrelin

Answer 29

Stomach hormone

Stimulates:
Food intake 
“Hunger Hormone”
GH secretion from the pituitary
Adiposity

Causes fat cells to grow.
Also regulates emotion and anxiety, so you can’t just block it.
And if you did, other hunger hormones would take over.

Question 30

Leptin

Answer 30

Secreted from adipose (fat) cells

Acts on receptors in the CNS and at other sites to:
Induce energy expenditure
Inhibit food intake (“satiety hormone”)

Animal without leptin became morbidly obese.
Some people have bodies and brains have receptors that don’t respond to leptin, and become obese.

Question 31

Adrenal Glands

Answer 31

Bilateral glands above kidneys

Like the pituitary, adrenals are 2 glands with distinct embryological origins:
Adrenal medulla (inner)
Adrenal cortex (outer)

The adrenal glands develop from 2 separate embryological tissues: the neural crest ectoderm and the intermediate mesoderm.
The medulla originates from neural crest cells migrating from sympathetic ganglion. Mesodermal cells then surround the medulla.
The adrenal cortex develops from the intermediate mesoderm. The fetal cortex develops in the centre, with the permanent cortex surrounding it.

Both parts of the adrenals work together to regulate metabolism and cope with stress

Question 32

Hormones of the Adrenals

Answer 32

Epinephrine & Norepinephrine:
Released in response to stress and activation of the SNS
Affect the circulatory and metabolic systems to prepare the body for action and cope with emergencies (“flight or flight” response)

Glucocorticoids
e.g. Cortisol: humans; corticosterone; rodents and other animals.
Released in response to stress.
Affects carbohydrate metabolism resulting in increased blood levels of glucose.

Mineralocorticoids
e.g. Aldosterone
Primarily responsible for causing the kidney to retain sodium and reduce the urine production.

Sex hormones
e.g. Testosterone
Congenital Adrenal Hyperplasia

Question 33

Gonads

Answer 33

Male: testes
Female: ovaries
Forms from the same tissue

Two functions compartmentalized to different cell types:

• -Production of steroid hormones
• -Production and maturation of gametes (sperm & eggs)

Males: constant in function
Females: cyclic in function

Function of gonads regulated by gonadotropins (LH & FSH) from the anterior pituitary

The hormones of the gonads are important for:

• -Gamete maturation
• -Development for secondary sex characteristics
• -Reproductive behaviors

Question 34

Testes

Answer 34

Male gonads

Sertoli cells: produce sperm; a majority of the testes cells are stroll cells

Seminiferous tubules: sperm maturation

Leydig cells: hormone-producing cells

Question 35

Primary Testicular Hormones

Answer 35

Androgens including testosterone, androstenedione, and dihyrdotestosterone

Sperm production

Maintenance of genial tract and accessory sex organs

Support secondary sex characteristics; like a deep voice, musculature, etc.

Influence metabolism

Sexual, aggressive, and other social behaviors

Question 36

Ovaries

Answer 36

Female gonads

3 subunits:
Follicles: contain developing egg.
Corpora lutea: structures that develop from follicles after egg is released.
Stroma: supporting tissue.

Prior to ovulation: FSH (tropic hormone) stimulates follicle development, and mature follicles secrete estrogens

After ovulation: LH (tropic hormone) follicles to enlarge and differentiate into luteal cells and combine with theca cells to form the corpus luteum which secretes progestins

Question 37

Primary Ovarian Hormones

Answer 37

Estrogens (i.e. estradiol):
Affect genital tract
Induce secondary sex characteristics
Water metabolism & retention (bloating)  
Calcium metabolism
Sexual and maternal behavior

Progestins:
Maintaining pregnancy
Sexual behavior

Question 38

A Cautionary Note

Answer 38

Sex hormones, they should not be considered strictly male or female.

The two sexes differ in the concentrations of circulating androgens and estrogens.

The brain can convert androgens into estrogens

The ovaries make a small but an important amount of androgens

The testes make a small but an important amount of estrogens

Question 39

Classes of Hormones

Answer 39

Proteins and Peptides
Steroids
Monoamines (class of neurotransmitter and hormones)
Lipid-based (prostaglandins)

Question 40

Steroid Hormone Synthesis

Answer 40

Main sources: adrenal, gonads and brain

Structure: three 6-carbon rings plus one conjugated 5-carbon ring.
This chemical structure is identical among all vertebrate species

Different steroid hormones vary in the number and types of atoms attached to these rings

All steroid hormones are derived from cholesterol that is made from acetate by the liver

Question 41

Prohormone

Answer 41

a molecule that can act as a hormone itself or can be converted into another hormone

Sometimes one hormone is a precursor for another hormone, and sometimes they can convert back and forth.

Aromatization conversion of T to estrogens through by the enzyme aromatase
Testosterone is a prohormone for estradial

Question 42

Steroid Hormones

Answer 42

Fat soluble (i.e. can easily move through cell membranes, don’t need carries or channels)

NOT soluble in water thus require carrier proteins for transport through the blood to their target tissue

Receptors located inside the cells (cytosol or nucleus)

Hormone receptors form dimers, and translocate to the nucleus.

Hormone-receptor complexes bind to hormone response elements on DNA, regulate transcription

Have slow but lasting effects

Parking spot on the DNA: HRE’s (hormone response elements)

Question 43

Non-genomic effects of steroid hormones

Answer 43

Steroids can also have a brief, rapid effect on some neurons without affecting gene expression

Alterations in neuronal excitability

Involves receptors found in the membrane

Question 44

Receptor Isoforms

Answer 44

A version of a hormone receptor with slight differences in structure that give it different functional properties

Estradiol binds equally well to both receptors
Estrone binds preferentially to the alpha receptor
Estriol binds preferentially to the beta receptor

Question 45

Protein & Peptide Hormones

Answer 45

Made up of individual amino acids
Peptide (small)
Protein/polypeptide (large)

Includes:
Neurohormones of the hypothalamus
Tropic hormones of the anterior pituitary
Posterior pituitary hormones
Parathyroid hormone
Calcitonin
Gastrointestinal hormones
Ghrelin
Leptin
Pancreatic hormones