Hormones of the Body

Akrum Hamdy

The Hypothalamus & the Pituitary Gland-- Master Endocrine Glands!

The Hypothalamus:• Located in the brain,

this region controls most endocrine secretions

• Mainly regulatory hormones are released here. Most control the pituitary gland

The Pituitary Gland• Descending from the

hypothalamus, this gland has two halves: anterior & posterior

• The anterior half secretes mainly regulatory hormones

• The posterior half secretes hormones, but manufactures none

Hormones secreted by the Hypothalamus & Anterior Pituitary Gland

Hypothalamus Anterior Pituitary

GHRH (GH-releasing) GH (growth hormone)

SS (somatostatin, GH-inhib) “

CRH (corticotropin-rel) ACTH (adrenocorticotropic)

GnRH (gonadotropin-rel) LH (luteinizing hormone)

“ FSH (follicle-stimulating)

PRH (PRL-releasing) PRL (prolactin)

PIH (PRL rel-inhibiting) “

TRH (thyrotropin-rel) TSH (thyroid stimulating)

What do these anterior pituitary hormones do?

Growth Hormone:• stimulates cells to grow and

divide• increases amino acid

transport rate and protein synthesis

• increases fat metabolism

Typically, GH is secreted during sleep.

GH secretion increases when malnourished

GH influences bone growth via somatomedin:

GH in blood

GH arrives in liver

liver secretes somatomedin

cartilage divides

bones grow!

Problems with GH

• Too much GH in children leads to gigantism

• Too much GH in adults leads to acromegaly

• Too little GH in children leads to dwarfism

Other Anterior Pituitary Hormone Functions

ACTH:• works on the cortex of the

adrenal gland, influencing the release of cortisol

• stress can increase CRH secretion which will increase ACTH secretion

• negative feedback when adrenal cortex hormones in blood decrease CRH secretion

LH & FSH:• LH in females and in males leads

to sex hormone secretion

• FSH in females causes growth and development of egg cell-containing follicles in the ovary, and causes estrogen secretion

• FSH in males instigates sperm production

• both hormones are regulated by GnRH, which is not significant in concentration until puberty

More Anterior Pituitary Hormone Functions

PRL:• In females, PRL promotes

lactation

• In males, PRL decreases LH secretion (note that too much PRL would then decrease androgen levels and cause sterility)

• Controlled by both PRH and PIH

TSH:• works on thyroid gland to

either cause or inhibit its secretion of hormones

• works on thyroid gland to affect its growth (too much TSH leads to a goiter)

• negative feedback via thyroid hormones in blood

• stress or cold temperatures can change TSH secretion

The Posterior Pituitary Lobe

No hormones are made here. They are made in the hypothalamus and just released here.

Two peptide hormones are released from the posterior pituitary lobe (the neurohypophysis):

• ADH (antidiuretic hormone or vasopressin)

• OT (oxytocin)

Function of Posterior Pituitary Lobe Hormones

ADH:• as an “antidiuretic,” ADH

decreases urine formation by having kidneys conserve water

• also can contract smooth muscle cells, as found in blood vessels-- this causes an increase in blood pressure

• ADH release triggered by osmoreceptors and inhibited by stretch receptors in blood vessels

OT:• In females, contracts the

uterine wall smooth muscles

• In females, helps to eject milk when lactating

• No known function in males, although in both males and females, OT can have some antidiuretic effects

The Thyroid Gland

Structure: This bilobed gland contains many follicles. A follicle is a group of cells encircling a lumen. The lumen contains material called colloid (a glycoprotein) within it. As hormones are produced by the cells, the hormones are either released into the colloid or directly into the blood.

There are also extrafollicular hormone-secreting cells, called C cells. These are found between lumina.

Hormones Produced:• Thyroxine (T4) made in follicle

• Triiodotyronine (T3) made in follicle

• Calcitonin made by C cells

About the Thyroid Hormones...T3 and T4:• Function: metabolism regulation

(break down carbohydrates and fats, synthesize proteins)

• Can only be made by follicular cells when iodides are available

• Somewhat hydrophobic and get carried by proteins in the blood.

• Controlled by anterior pituitary lobe TSH

• T3 more effective, T4 more abundant

Calcitonin:• Function: decrease blood

calcium levels and blood phosphate levels (by helping them get deposited in bone, and by stimulating excretion of them by kidneys)

• Controlled by blood calcium levels and digestive chemicals

Problems with the Thyroid GlandHyperthyroidism:• high metabolic rate, hyperactivity, sensitivity to heat, protruding eyes

• Grave’s disease: when hyperthyroidism is due to an autoimmune problem (TSH is mimicked by autoantibodies)

Hypothyroidism:• in the adult: low metabolic rate, sensitivity to cold, sluggishness

• in an infant: cretinism-- stunted growth, mental retardation, abnormal bone formation

• Hashimoto’s disease: when hypothyroidism is due to an autoimmune problem (autoantibodies attack and destroy follicular cells)

• goiter: no T3 and T4 can be made because not enough iodides were ingested.

Let’s Review:

What glands and hormones did welearn about so far?

Hypothalamus & Anterior PituitaryHypothalamus Anterior Pituitary

GHRH (GH-releasing) GH (growth hormone)

SS (somatostatin, GH-inhib) “

CRH (corticotropin-rel) ACTH (adrenocorticotropic)

GnRH (gonadotropin-rel) LH (luteinizing hormone)

“ FSH (follicle-stimulating)

PRH (PRL-releasing) PRL (prolactin)

PIH (PRL rel-inhibiting) “

TRH (thyrotropin-rel) TSH (thyroid stimulating)

Your book’s review diagram:

Posterior Pituitary & Thyroid Gland

Posterior Pituitary:

• ADH

• OTBoth of these hormones are

made in the hypothalamus… their release is regulated by the brain.

Thyroid Gland:

• T3 (regulated by TSH)

• T4 (regulated by TSH)

• calcitonin (NOT regulated by the pituitary!)

Moving on to More Glands!

We still have the following left:• Parathyroid Gland• Adrenal Gland: both the Medulla and the Cortex

• Pancreas

• Pineal

• Other, including thymus and reproductive glands

Parathyroid Gland• This gland only

secretes one hormone: Parathyroid Hormone (or PTH)

• PTH function (we began learning this when

we studied bone):– increases blood

calcium (Ca2+) levels and decreases blood phosphate (PO4

2-) levels

PTH function (continued)

• How does PTH work?– PTH causes Ca2+ & PO4

2- to be released from bone into blood (by increasing osteoclast activity)

– PTH causes the kidneys to remove PO42- ions from the

urine

– PTH increases vitamin D production, so that you absorb more Ca2+ during digestion

• PTH is regulated by blood calcium levels-- not by other glands!

Adrenal Glands

An adrenal gland is found on top of each kidney. Each adrenal gland has two regions that carry out separate functions!

•The adrenal medulla•The adrenal cortex

We will cover each of these two regions separately in the next few slides.

The Adrenal Medulla

Acts very much like a part of the sympathetic nervous system (fight or flight)

Secretes two amines:– norepinephrine (20%)– epinephrine (80%)

Stimulated by preganglionic neurons directly, so controlled by the hypothalamus as if part of the autonomic nervous system, NOT by tropic hormones

The Adrenal Cortex

Acts like a regular endocrine organ

Secretes many hormones, but most importantly secretes the following steroids:– aldosterone– cortisol– sex hormones

Aldosterone and cortisol require further explanation (while sex hormone production will be covered later this semester)

More about Adrenal Cortex HormonesAldosterone:Considered a mineralocorticoidRegulates “mineral electrolyte” levels in

the blood (for example: Na+ and K+ ions)

How is aldosterone controlled?

– blood plasma ion concentrations affect its secretion directly (but not always strongly)

– kidney secretes renin in response to altered electrolyte levels, which triggers angiotensin activation in the blood, which leads to aldosterone secretion

– ACTH from the anterior pituitary can cause aldosterone secretion

Cortisol:Considered a glucocorticoidOverall effect of cortisol:

• Helps to keep blood glucose concentration within a normal range between meals

Specific actions of cortisol:

• increases amino acid concentration in the blood (by inhibiting protein synthesis in select tissues)

• promotes use of fat for energy production in our bodies (rather than glucose)

• stimulates the liver to synthesize glucose (not from carbohydrates, but from amino acids and glycerol), called gluconeogenesis

The Pancreas• This gland has both endocrine and exocrine

functions… we’ll only cover the endocrine portion now (exocrine is for digestion)

• The endocrine portion of the gland contains three types of cells, each making a different hormone, arranged into groups called Islets of Langerhans– alpha cells: secrete glucagon

– beta cells: secrete insulin

– delta cells: secrete SS (somatostatin)

• Note that these pancreatic hormones are involved in blood glucose regulation, and problems with them can lead to diabetes.

Blood Glucose Regulation by the PancreasGlucagon:

It works on the liver to cause the production of glucose via:– glycogenolysis

– gluconeogenesis

It is regulated by blood glucose levels directly:– secreted when blood glucose

drops (before next meal)

Prevents hypoglycemia

Insulin:

It works on the liver to remove glucose from the blood via:– making glycogen

– preventing gluconeogenesis

– increasing glucose transport into cells

It is also regulated by blood glucose levels directly

Prevents hyperglycemia

Note: glucagon and insulin work in opposition, and their combined effects control blood glucose

Pineal Gland

Secretes only one hormone: melatonin

Involved in your circadian rhythm (your recognition of day and night times):– melatonin secretion decreases in the day– melatonin secretion increases at night

Melatonin is also involved in longer rhythms, like monthly and seasonal… and is thought to be involved in the female menstrual cycle and maybe in the onset of puberty

Other Endocrine Glands

• Thymus Gland: secretes thymosins which are involved in white blood cell production

• Reproductive glands (the gonads): the ovaries and the testes produce sex hormones

• Others: too specific for now, we’ll get to them as we continue this semester.