Lecture 7: Endocrine System

Functions of Endocrine System

Organs that secrete hormones → blood stream

• Controls the function of other target organs

• A form of long distance communication

Primary Endocrine Organs

1. Hypothalamus

   1. "head honcho”

   2. Found in brain

2. Pituitary

   1. “2 parts, anterior and posterior”

   2. Also found in the brain

3. Pineal

   1. Found in brain

4. Thyroid and parathyroid

5. Thymus

6. Adrenal gland

7. Pancreas

8. Testes and ovaries

Structure of Hypothalamus

Neural secretory cells and nuclei that connect to the pituitary gland

• Neural secretory cells: neurons that secrete hormones at axon terminal

• “Nuclei = anatomical nuclei = several soma, or cell bodies, in the CNS = nucleus

  • referring to several soma of the secretory cells

Function of Hypothalamus

Controls release of pituitary hormones

• Secretes: releasing and inhibiting tropic hormones to the anterior pituitary gland

• Tropic hormones: secreted from one gland, causes another gland to secrete another hormone

“Hypothalamus controls the release of hormones in both the posterior pituitary and anterior pituitary. Anterior = uses different tropic hormones and specifically two capillary blood paths”

What are the two hypothalamus connections?

1. Posterior pituitary

2. Anterior pituitary

Note for Hypothalamus - Posterior pituitary (PP) connection

*no endocrine (green) cells

• Just axons and singular capillary bed

Hypothalamus - Posterior Pituitary (PP) Connection

1. Neurons in hypothalamus synthesizes (produces) and secretes hormones

   1. Supraoptic nucleus (LHS): oxytocin

   2. Paraventricular nucleus (RHS): Anti-diuretic hormone (ADH)

2. Hormones stored in terminal vesicles (in PP, at the tip of axon terminals)

3. When stimulated (by hypothalamus) → vesicles release hormones in capillary beds of PP

*KNOW: Sample of what could be asked about Hypothalamus - PP connection

• Produced by _______ nucleus in hypothalamus

  • Supraoptic nucleus (LHS)

  • Paraventricular (RHS)

• Stored in terminal vesicles of PP

• Released from PP even though it’s controlled by hypothalamus

Hypothalamus - Anterior Pituitary (AP) Connection

Portal System

*Uses Tropic hormone to control AP

1. Stimulated neurosecretory cells release hormones in 1st capillary bed (found in infundibulum)

2. 1st capillary bed → portal vein → 2nd capillary bed (in AP)

3. Hormones exit capillaries → stimulate AP endocrine cells

4. AP endocrine cells secrete hormones in (second) capillaries → body for circulation

Parts of the Pituitary Gland

1. Posterior

2. Anterior

Structure of Posterior Pituitary Gland

Neural tissue (axon terminals) from hypothalamus

• “Neural extension of the hypothalamus”

• “Not a true endocrine gland”

Secretions of Posterior Pituitary Gland

1. Anti-diuretic hormone (ADH) or vasopressin

   1. Targets: kidney

   2. Results: Increased water reabsorption, lower urine volume

      1. *Diuretic = makes you urinate more

      2. *Anti-Diuretic = not make you urinate as much

      3. *ADH = causes you to retain fluids vs. turning into urine = less urine

2. Oxytocin

   1. Targets: uterus and breasts

   2. Results:

      1. Uterine contraction

      2. Milk expulsion

         1. getting milk out of the breast, different from milk production

Structure of Anterior Pituitary Gland

epithelial tissue

Secretions of Anterior Pituitary Gland

1. Prolactin

2. Thyroid stimulating hormone (TSH)

3. Adrenocorticotropic hormone (ACTH)

4. Growth hormone (GH)

5. Luteinizing hormone (LH)

6. Follicle stimulating hormone (FSH)

*Anterior pituitary gland always controlled by the hypothalamus, so another hormone (tropic) was released from hypothalamus that controlled release of ^

Prolactin

Controlled by hypothalamus:

• Prolactin releasing hormone (PRH) (TROPIC)

• Prolactin inhibiting hormone (PIH) or dopamine

Acts on: breasts

Result: milk secretion (production), mammary gland development (of breasts)

Thyroid Stimulating Hormone (TSH) (TROPIC)

Controlled by hypothalamus:

• Thyrotropin releasing hormone (TRH) (TROPIC)

Acts on: thyroid gland

Results: release thyroid hormones → increased metabolism

Adrenocorticotropic Hormone (ACTH) (TROPIC)

Controlled by hypothalamus:

• Corticotropin releasing hormone (CRH) (TROPIC)

Acts on: adrenal gland

Results: releases glucocorticoids (cortisol) → stress responses

Growth Hormone (GH)

Controlled by hypothalamus:

• Growth hormone releasing hormone (GHRH) (TROPIC)

• Growth hormone inhibiting hormone (GHIH) or somatostatin

Acts on: Liver and cells

Results:

• Liver: releases insulin-like growth factors (somatomedins)

  • *will then act on cells and cause to grow

• Cells: signals growth and metabolism

*GH is only tropic if it goes to the liver

Luteinizing Hormone (LH) (TROPIC)

Controlled by hypothalamus:

• Gonadotropin releasing hormone (GnRH) (TROPIC)

Acts on: ovaries and testes

Results: ovulation, secretion of sex hormones

Follicle Stimulating Hormone (FSH)

Controlled by hypothalamus:

• Gonadotropin releasing hormone (GnRH) (TROPIC)

Acts on: ovaries and testes

Results: development of egg and sperm

Structure of Pineal Gland

Epithelial tissue in brain

What does the pineal gland secrete?

melatonin

Results of secretion from pineal gland:

Regulates circadian rhythm

*helps you sleep

*as it gets darker, pineal gland will secrete melatonin

Structure of Thyroid

Butterfly structure, ventral (front) surface of trachea

Secretions of Thyroid and its Results

Secretes:

1. Tetraiodothyronine (T4) and Triiodothyronine (T3)

2. Calcitonin

   1. “tone down the Ca2+”

Results:

1. Increase metabolism

2. Lowers Ca2+ levels in blood, deposition in bone

   1. “puts Ca2+ from blood into bone”

Structure of Parathyroid

4 small glands behind the thyroid

Secretions of Parathyroid and its Results

Secretes: parathyroid hormone (PTH)

Results: increase blood Ca2+ levels

• “thyroid produces calcitonin, decreases Ca2+ levels”

  • “parathyroid found on opposite side of the thyroid. PTH will increase Ca2+ levels”

• “PTH breaks down bone. Takes calcium from bone and it causes Ca2+ to be released back into the blood”

Structure of Thymus

Two-lobed gland in front of the heart

Secretion of the Thymus and its Results

Secretes: thymosin

Results: T-cell functional regulation

• “large when you are younger, smaller as you grow”

• “T-cells = type of WBC. Develops and gets training in thymus”

Structure of Adrenal Gland

Multilayered glands above kidneys

1. Cortex

2. Medulla

“suprarenal gland”

Cortex of Adrenal Gland

Outer layer of adrenal gland

Secretions of Adrenal Cortex and its Results

Secretes:

1. Mineral corticoids (aldosterone [regulates BP by increasing])

2. Glucocorticoids (cortisol)

3. Androgens (sex hormones that help promote sex drive)

Results:

1. Stimulate Na+ reabsorption, K+ secretion in kidneys

2. Catabolism of fats and proteins, raise blood glucose, stress response

3. Promotes sex drive

Medulla of Adrenal Gland

Inner core of adrenal gland

Secretions of Adrenal Medulla and its Results

Secretes:

• Epinephrine

• Norepinephrine

Results:

• Increased heart rate

• Mobilization of energy sources

Structure of Pancreas

Exocrine and endocrine gland below stomach

1. Exocrine cells: acinar cells

   1. “releases things into external environment”

   2. “releases a lot of digestive enzymes”

2. Endocrine cells: Islets of Langerhans

*endocrine = release hormones into blood

Function of Exocrine Cells

Secrete enzymes to GI tract

• digestive enzymes

Types of Endocrine Cells

1. Alpha cells

2. Beta cells

3. Delta cells

4. F cells

Characteristics of Alpha Cells

Secretes: glucagon

• “…is secreted when glucose is gone to raise blood glucose levels”

Results:

• raises blood glucose

• glycogenolysis

  • “breakdown glycogen”

Characteristics of Beta Cells

Secretes:

• insulin

Results:

• lowers blood glucose

• promotes energy storage

  • “stores as glycogen”

Characteristics of Delta Cells

Secretes:

• somatostatin

  • “statin stops”

Results:

• Inhibits secretion of pancreatic hormone

  • “alpha and beta cells”

Characteristics of F Cells

Secretes:

• pancreatic polypeptide

Results:

• Inhibits pancreatic exocrine secretions

  • “stop and work on your acinar cells and stop them from secreting digestive enzymes”

Testes in Males

Secretes:

• Androgens

Results:

• Sperm production

• Sex drive

• Secondary sex characteristics (deepening of voice, muscle development)

Ovaries in Female

Secretes:

• Estrogens

Results:

• Follicular development (development of follicle/egg)

• Secondary sex characteristics (widening of hips, development of breast tissue)

The portal system connects the…

A) hypothalamus and posterior pituitary

B) anterior pituitary and posterior pituitary

C) hypothalamus and anterior pituitary

D) pineal gland and the hypothalamus

Which of the following is not a tropic hormone?

A) GnRH: Gonadotropin releasing hormone

B) TSH: Thyroid stimulating hormone

C) TRH: Thyrotropin releasing hormone

D) PTH: Parathyroid Hormone

Epinephrine is secreted from…

A) Thyroid

B) Adrenal cortex

C) Adrenal medulla

D) Anterior pituitary

Which cells of the pancreas secretes glucagon?

A) Beta cells

B) Delta cells

C) F cells

D) Alpha cells

Oxytocin….

A) originates from the paraventricular nucleus

B) is released by the posterior pituitary

C) is the same as vasopressin

D) all of the above