Chapter 17: Endocrine System

What is the Endocrine System?

• A system of ductless glands

• secrete messenger molecules called hormones

• interact with nervous system

• controls and integrates the functions of other organs systems

How do hormones travel?

Hormones travel to distant body cells and signal characteristic physiological responses

What does the endorcrine system maintain?

Maintains homeostasis, controls growth, metabolism, stress defenses, blood chemistry, etc

Which endocrine organs are PURE

• Pituitary

• Pineal

• Thyroid

• Parathyroid

• Adrenal Glands

Which endocrine organs are REGULAR (not pure)

• Hypothalamus, thymus, pancreas, and gonads

True or False, are endocrrine organs richly vascularized?

true

Hypothalamus

Pineal gland

pituitary gland

thyroid

Parathyroid glands

Thymus

adrenal glands

pancreas

Gonads (ovaries and testes)

What are steroid hormones

Steroid hormones are a class of hormones derived from cholesterol, which is a type of lipid

• Examples include estrogen, progesterone, androgens, cortisol, and aldosterone

What are non-steroidal hormones?

Non-steroidal hormones are derived from protein/peptides, amino acids, or fatty acid derivatives

Examples of non-steroidal hormones include:

• Glycoproteins like follicle stimulating hormone (FSH), luteinizing hormone (LH), and human chorionic gonadotrophin (hCG)

• Polypeptides such as prolactin, growth hormones, insulin, and glucagon

• Monoamines like epinephrine and norepinephrine

• Eicosanoids, which are fatty acid derivatives, such as prostaglandin

Which non-steroidal hormones is dervied from protein/peptides?

1. Glycoproteins: Follicle Stimulating Hormone (FSH), Luteinzing Hormone (LH), and Human Chorionic Gonadotropin (hCG)

2.Polypeptides: Prolactin, Growth Hormone (GH), Insulin, and Glucagon

Which non-steroidal hormones is dervied from amino acids?

Monoamines: epinephrine, norepinephrine

Which non-steroidal hormones is dervied from fatty acids derivatives?

Eicosanoids: prostaglandin

Basic Hormone Actions

• Travel in the blood

• Affect only target cells with matching receptors

• Can cause different effects in different cells

• Act as triggers, not instructions — cells are preprogrammed

Control Hormone Secretion; name the 3 main types of triggers

1. Humoral

2. Neural

3. Hormonal

What is humoral hormone control? w/ example

Hormones released due to changes in blood levels of ions/nutrients

• Example: If calcium levels drop, it releases parathyroid hormone (PTH) to raise calcium levels.

What is neural hormone control? w/ example

Hormones released by nerve signals

• During stress, the sympathetic nervous system signals the adrenal medulla to release epinephrine (adrenaline) for the "fight or flight" response.

What is hormonal hormone control? w/ example

One hormone triggers another hormone to be released

• Hypothalamus releases TRH

• TRH signals pituitary to release TSH

• TSH signals thyroid gland to release thyroid hormones

How is hormone secretion controlled?

• Controlled by feedback loops

• If hormone level drops below minimum, secretion increases

• If hormone level exceeds maximum, secretion stops

How does the hypothalamus control the anterior pituitary?

Hypothalamus controls hormone release from the anterior pituitary which includes the releasing hormones and inhibiting hormones

What are releasing hormones?

Hormones from the hypothalamus that stimulate the anterior pituitary to release its hormones

What are inhibiting hormones?

Hormones from the hypothalamus that stop or reduce hormone release from the anterior pituitary

How many major hormones does the pituitary gland secrete?

The pituitary gland secretes nine major hormones.

Where is the pituitary gland located?

Located in the hypophyseal fossa, a depression in the Sella turcica of the sphenoid bone.

What are the two basic divisions of the pituitary gland?

• Adenohypophysis (anterior pituitary)

• Neurohypophysis (posterior pituitary)

What are the anterior lobe hormones (adenohypophysis)

1. Growth Hormone (GH)

2. Thyroid stimulating hormone (TSH)

3. Adrenocorticotropic hormone (ACTH)

4. Follicle-stimulating hormone (FSH)

5. Luteinizing hormone (LH)

6. Prolactin (PRL)

What are the effects of hyposecretion and hypersecretion AND regular function in Growth Hormone

• Low Levels: dwarfism in children

• High Levels: giantism in children; acromegaly in adults

Function: promotes growth of bones, muscles and tissues

What are the effects of hyposecretion and hypersecretion AND regular function in Thyroid-stimulating hormone

• Low levels: cretinism in children; myxedema in adults

• High levels: hyperthyroidism; effects similar to those of Graves’ disease, in which antibodies mimic TSH

  Function: Thyroid gland: stimulates thyroid gland to release thyroid hormones

What are the effects of hyposecretion and hypersecretion AND regular function in Adrenocorticotropic hormones (ACTH)

• Low levels: rare

• High levels: Cushing’s disease

  Function: Stimulates the adrenal cortex to release cortisol and other glucocorticoids

What are the effects of hyposecretion and hypersecretion AND regular function in Follicle-stimulating hormone

• Low: failure of sexual maturation

• High: No important effects

Function: women: helps eggs mature (inside follicles); men: help make sperm (follicle and sperm helper)

What are the effects of hyposecretion and hypersecretion AND regular function in Luteinizing hormone

• Low levels: Failure of sexual maturation

• High levels: no important effects

Function: women: triggers ovulation (release of eggs) and makes the body produce progesterone; men: tells the testes to make testosterone

What are the effects of hyposecretion and hypersecretion AND regular function in Prolactin

• Low levels: poor milk production in nursing women

• High Levels: inappropriate milk production; cessation of menses in females; impotence in males

Function: prolactin makes breast milk after birth

What is the posterior pituitary (neurohypophysis), and is it part of the brain?

• The posterior pituitary (neurohypophysis) is structurally part of the brain.

• It does not make hormones, but stores and releases hormones made by the hypothalamus.

What is the role of the posterior pituitary in hormone production?

The posterior pituitary does not produce hormones.
It stores and releases hormones that are made by the hypothalamus.

Which two hormones does the Posterior Lobe store and secrete?

Antidiuretic hormone and Oxytocin

What is Antidiuretic Hormone (ADH), and what are its functions?

ADH (Antidiuretic Hormone), also called vasopressin, is secreted by the posterior pituitary.
It targets the kidneys and arterioles to:

• Help retain water

• Regulate fluid volume

• Increase blood pressure

Low levels: Diabetes insipidus

High levels: Syndrome of inappropriate ADH secretion

What is oxytocin and what are its effects?

Oxytocin is secreted by the posterior pituitary.
It causes:

• Uterine contractions during labor

• Milk ejection during breastfeeding

Low and High Levels: unknown

What are the functions of the thyroid gland and the hormones it produces?

The thyroid gland produces two hormones with distinct functions:

• Thyroid Hormone (TH):

  • Regulates metabolic rate

  • Affects energy use, growth, and development

• Calcitonin:

  • Lowers blood calcium levels

  • Inhibits osteoclasts (bone breakdown)

  • Enhances calcium excretion by kidneys

What is the difference between follicular cells and parafollicular cells in the thyroid gland?

• Follicular Cells:

  • Produce Thyroid Hormone (TH)

  • Function: Regulate metabolic rate

• Parafollicular Cells (C cells):

  • Produce Calcitonin

  • Function: Lower blood calcium levels by inhibiting osteoclasts and increasing calcium excretion by the kidneys

Disorders of Thyroid

Low Levels: person always cold, gains weight, but doesn’t feel hungry

High Levels: Person is “hot”, loses weight, very hungry, anxious. Must ablate thyroid

• Goiter appears on the neck and it is unknown if it due to hyper or hypo- thyroidism

What is the function of the parathyroid gland and its main hormone?

he parathyroid gland contains chief cells that produce parathyroid hormone (PTH). And also contains oxyphil cells

Function of PTH:

• Increases blood calcium (Ca²⁺) levels by:

  • Stimulating osteoclasts to break down bone

  • Enhancing calcium reabsorption in kidneys

  • Promoting calcium absorption in the intestines (via vitamin D activation)

What are chief cells in the parathyroid gland and what is their function

• Chief cells are the main functional cells of the parathyroid gland.

• They produce parathyroid hormone (PTH)

What are oxyphil cells in the parathyroid gland and what is their function?

• Oxyphil cells are larger, less numerous cells in the parathyroid gland.

• Their exact function is unknown

What are the main functions of the pancreas?

• Exocrine function:

  • Acini cells secrete digestive enzymes into the small intestine to help break down food.

• Endocrine function:

  • Pancreatic islets (islets of Langerhans) secrete hormones (like insulin and glucagon) that regulate blood sugar levels.

What are the endocrine cell types?

Alpha cells and beta cells

What is the function of Alpha cells in the pancreas?

Secrete glucagon: signals the liver to release glucose from glycogen which raises blood sugar

(in other words, the glucagon (hormone) goes to the liver to break glycogen (sugar) back to glucose (sugar), and it happens when sugar levels are low and alpha cells send signals to receive the glucose that is stored to be used)

What is the function of Beta cells in the pancreas?

Secrete insulin: signals most body cells to take up glucose from the blood which lowers blood sugar

(in other words, beta cells tell the glucose to go get stored in the liver which then gets transformed into glycogen)

What causes diabetes mellitus?

Diabetes mellitus is caused by:

• Insufficient secretion of insulin, or

• Resistance of body cells to the effects of insulin

What is Type I Diabetes Mellitus?

• Develops suddenly, usually before age 15

• Caused by a T cell-mediated autoimmune response

• Destroys beta cells in the pancreas

• Leads to little or no insulin production

What is Type II Diabetes Mellitus?

• Known as adult-onset diabetes

• Usually occurs after age 40

• Body cells have lowered sensitivity to insulin

• Can be controlled by dietary changes and regular exercise

What are the two main parts of the adrenal glands?

• Adrenal medulla: a knot of nervous tissue

• Adrenal cortex: bulk of the gland, composed of three layers:

  • Zona glomerulosa

  • Zona fasciculata

  • Zona reticularis

What cells make up the adrenal medulla and what do they secrete?

• Chromaffin cells: modified postganglionic sympathetic neurons

• Secrete catecholamines: norepinephrine and epinephrine

• Active in the fight, flight, and fright response

What hormones are secreted by the adrenal cortex and their functions?

• All hormones are steroids and grouped into:

  • Mineralocorticoids:

    • Aldosterone (zona glomerulosa)

  • Glucocorticoids:

    • Cortisol (zona fasciculata and zona reticularis) — helps deal with stress

  • Androgens:

    • Dehydroepiandrosterone (DHEA) (zona reticularis) — converted to testosterone and estrogen; may help with stress, immune system, and mood

What are the Gonads

Main source of sex hormone- testes and ovaries

What do the male gonads secrete and what are their functions?

• Interstitial cells secrete androgens, primarily testosterone

• Testosterone:

  • Promotes sperm formation

  • Maintains secondary sex characteristics (like facial hair, deep voice, muscle mass)

What hormones do the female gonads secrete and what are their functions?

Ovaries secrete:

• Estrogen:

  • Maintains secondary sex characteristics

  • Signals uterine mucosa to repair after menstruation

• Progesterone:

  • Produced by follicular granulosa cells and corpus luteum

  • Prepares the uterus for pregnancy

What is the function of the thymus gland and what happens to it after puberty?

• Produces and secretes thymosin, a hormone essential for T cell development and production

• Largest in children

• Shrinks and is replaced by fat after puberty

What hormone does the pineal gland secrete and when?

• Secretes melatonin

• Mainly produced in the absence of light (at night)

• Helps regulate sleep-wake cycles (circadian rhythm