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68 Cards in this Set

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Another name for the pituitary gland is?
Hypophysis
What is the the adenohypophysis?

How is it formed?
Anterior Pituitary

Via the pinching off of Rathke's Pouch, forming the pars distalis, pars intermedia, pars tuberalis.
What is the neruohypophysis?

How is it formed?
Posterior Pituitary

Arises as a down growth of the diencephalon.
Which part of the pitiutary has a direct connection with the hypothalamus?

What is the connection called?
Posterior Pituitary

Infundibulum (Hypophysial stalk, neural stalk)
What are the parts that make up the anterior pituitary?
1) Pars distalis
2) Pars tuberalis - the part that fuses to the infundibulum
3) Pars intermedia
What are the parts that make up the posterior pituitary?
1) Infundibulum
2) Pars nervosa
What 2 hormones are produced in the Pars nervosa?

Where are these hormones produced?
1) vasopressin ((AVP) aka antidiuretic hormone (ADH)
2) Oxytocin (OT)

hypothalamus - transported & stored in the pars nervosa - released into the peripheral circulation
Describe the blood supply of:

1) Anterior pituitary

2) Posterior pituitary
1) Portal System (no direct blood supply) - superior arteries supply the median eminence - capillaries, veins, capillaries, veins

2) inferior hypophyseal arteries (direct blood supply)
What are the cell types of the Anterior Pituitary?
I) Granules bind dyes
a) acid dyes
1) synthesize & release growth
hormone (GH)
2) synthesize & release prolactin
(PRL)
b) basic dyes
1) synthesize & secrete throid
stimulating hormone (TSH)
2) synthesize & secrete
adrenocorticotropic hormone
(ACTH)
3) produce & secrete both
Luteinizing hormone (LH) &
Follicle Stimulating hormone
(FSH)
II) Granules with little affinity for dyes
I) Chromophils
a) Acidophils
1) somatotrophs
2) lactotrophs
b) Basophils
1) Thyrotrophs
2) Corticotrophs
3) Gonadotrophs

II) Chromophobes
What hormones are secreted by the anterior pituitary?
1)
2)
3)
4)
5)
6)
1) ACTH
2) GH
3) TSH
4) FSH
5) LH
6) PRL
Which anterior pituitary or pars distalis hormones fit into these groups:

1) Corticotropin-related peptides

2) Somatomammotropins

3) Glycoproteins
1) ACTH, LPH, MSH

2) GH, PRL

3) LH, FSH, TSH
What are the Hypothalamic Releasing Hormones?

1) Binds to receptors on
gonadotrophs and stimulates the secretion of FSH and LH via PLC/IP3
mechanism.

2) Binds to receptors on thyrotrophs
and stimulates secretion of TSH via PLC/IP3.

3) Binds to receptors on the
somatotrophs and stimulates synthesis and release of GH via AC/cAMP

4) Binds to receptors on the
corticotrophs and stimulates ACTH secretion via AC/cAMP.

5) Inhibits the secretion of PRL

6) Human GH, prolactin, and placental lactogen (hPL), all share amino acid homologies and are thought to have a common ancesteral gene.
1) GnRH Gonadotropin-releasing hormone

2) TRH Thyrotropin-releasing hormone

3) GHRH Growth hormone-releasing hormone

4) CRH Corticotropin-releasing hormone

5) PIF Prolactin-inhibiting factor (Dopamine)

6) SS Somatostatin/ Growth hormone-inhibiting hormone
What hormones are gonadotropins?
FSH & LH
Follicle-Stimulating Hormone (FSH)
1. Chemical structure: Glycoprotein
hormone, composed of two
polypeptide chains α and β

2. Actions:
a) Promotes ovarian follicular
development & estrogen
secretion in females
b) Stimulates spermatogenesis in
males

3. Mechanism of Action: Increases
cAMP levels
Luteinizing Hormone (LH)
1. Chemical structure: Glycoprotein
hormone, composed of two
polypeptide chains α and β

2. Actions:
a) Stimulates ovulation
b) Stimulates corpus luteum
formation
c) Stimulates progesterone
secretion in females
d) Stimulates Leydig cells to
synthesize & secrete
testosterone in males

3. Mechanism of Action: Increases
cAMP levels.
Adrenocorticotropic Hormone (ACTH)
1. Chemical structure: Peptide (39
amino acids)

2. Actions: Stimulates synthesis and
secretion of glucocorticoids and
androgenic steroids from the
adrenal cortex.

3. Mechanism of action: Increases
cAMP levels.
Prolactin (PRL)
1. Chemical structure: Polypeptide
hormone (199 amino acids)

2. Actions: Stimulates milk production
in the breast

3. Mechanism of Action: Prolactin
actions are mediated by a dimeric
tyrosine kinase linked receptor.
Growth Hormone (GH)
1) Chemical Structure: Polypeptide
(191 amino acids)

2) Actions: Stimulates protein
synthesis and overall growth

3) Mechanism of Action: Receptor
has tyrosine kinase activity. Some
actions via Somatomedins (Insulin-
like growth factor [IGF]). The IGF
receptor has tyrosine kinase
activity.
Thyroid-Stimulating Hormone (TSH)
1) Chemical Structure: Glycoprotein
hormone, composed of two
polypeptide chains α and β

2) Actions: Increases synthesis and
secretion of thyroid hormones.

3) Mechanism of action: Increases
cAMP levels.
Oxytocin
1) Chemical Structure:
Peptide (nonapeptide)

2) Actions:
Causes milk ejection by stimulating contraction of myoepithelial cells of the mammary glands during nursing.
During labor, induces uterine muscle contraction.

3) Mechanisms of action: Exerts its action through IP3 mechanism.

4) Regulation:
Suckling stimulates oxytocin secretion.
Dilatation of the cervix stimulates oxytocin secretion.
Vasopressin or Antidiuretic Hormone
1. Chemical Structure:
Peptide (nonapeptide)

2. Actions and mechanisms:
a) Promotes resorption of water from collecting tubules in the kidney (V2 receptors) by increasing cAMP levels.

b) Elevates blood pressure by causing contraction of smooth muscle in arterioles (V1 receptors) via IP3.

4) Regulation:
↑ Serum osmolarity or ↓ blood volume -↑ADH secretion.
↓ Serum osmolarity or ↑ blood volume - ↓ADH secretion.
How is the anterior pituitary regulated?
1) Via releasing & inhibiting hormones from the hypothalamus.
Examples:
i) in cold weather, the hypothalamus stimulates the pituitary to secrete TSH
ii) in times of stress, it triggers the ACTH secretion, which indirectly mobilizes materials needed for tissue repair
iii) during pregnacy, it induces prolatin secretion so a woman will be prepared to lactate
How is the posterior pituitary regulated?
controlled by neuroendocrine reflexes - the release of hormones in response to signals from the nervous system

Examples:
i) suckling - stimulates nerve ending in the nipple, sensory signal are transmitted through the spinal cord & brainstem to the hypothalamus, then it goes to the posterior pituitary, causing the release of oxitocin = milk ejection
ii) dehydration - raises the osmolarity of the blood, which is detected by osmoreceptors - triggering ADH release, and ADH promotes water conservation.
iii) excessive blood pressure - strech receptors are stimulated in the heart & certain arteries - inhibiting ADH release, increasing urine output, and brings blood volume & pressure back to normal
What is an example of a positive feedback mechanism?
Oxytocin
Explaination:
Uterine streching sends a nerve signal to the brian the stimulates OT release. OT stimulates uterine contractions, which push the infant downward. This stretches the lower end of the uterus some more, which results in a nerve signal stimulating more OT release. This positive feedback continues until the infant is born.
What is negative feedback inhibition?
The pituitary stimulates another endocrine gland to secrete its hormone, and that hormone feeds back to the pituitary and inhibits further secretion of the tropic hormone.

Examples:
1) pituitary-thyroid axis
2) male gonadotropic axis
3) Corticotropic Axis
4) Lactotropic Axis
Thyrotropic Axis

TRH stimulates secretion of TSH by the anterior pituitary

Thyroid hormones (T3 and T4) inhibit secretion of TSH from the anterior pituitary
What is this mechanism?

Explain it.
Lactotropic Axis

PRL secretion is tonically inhibited by dopamine

TRH increases PRL secretion

PRL inhibits its own secretion by stimulating the hypothalamic release of dopamine
What is this mechanism?

Explain it.
In the tyrotropic axis, what happens when T3 and T4 are low?
There is high TRH & TSH because there is no inhibition.
Gonadotropin release is under negative feedback regulation by Progesterone, and Inhibins

Gonadotropin release is under negative or positive feedback regulation by Estrogen, depending of the time of the menstrual cycle.
What is this mechanism?

Explain it.
Female Gonadotropic Axis

1) When is the feedback
mechanism of estradiol positive?

2)When is it negative?
During ovulation estrogen stimulates (+) the release of LH & FSH. Otherwise is negative feedback.
Male Gonadotropic Axis

GnRH stimulates the anterior pituitary to secrete FSH and LH

Testosterone inhibits secretion of LH by an action on the hypothalamus and
anterior pituitary

Inhibin B (testis peptide) inhibits secretion of FSH from the anterior pituitary
What is this mechanism?

Explain it.
Corticotropic Axis

1) CRH (Corticotropin-releasing hormone) , originally named corticotropin-releasing factor (CRF), stimulates secretion of ACTH

2) Cortisol inhibits its own secretion by an action on the hypothalamus and on the anterior pituitary
What is this mechanism?

Explain it.
In vertebrates, the endocrine system and nervous system are physically and functionally linked by this region of the brain.
Hypothalamus- pituitary complex
Pars distalis
Is the largest of the 3 divisions and is the principal glandular part of the hypophysis. It contains different cell types that synthesize a broad spectrum of hormones which exert their effect on their target cells.
Pars tuberalis
Is an upwards extension of the pars distalis that partially surrounds the neural (infundibular) stalk.
Pars intermedia
Is poorly developed in the human but is more extensive in those vertebrates that exhibit marked changes in pigmentation or color. In this animals the pars intermedia produces melanocyte-stimulating hormone (alpha-MSH).
The pars nervosa
Composed of neural tissue and constitute the main part of the posterior pituitary.

It releases two hormones, vasopressin (AVP), also called antidiuretic hormone (ADH), and oxytocin (OT).

These two hormones are synthesized in the hypothalamus, but stored and released into the peripheral circulation by the pars nervosa.
Hypothalamic Functions:
1)
2)
3)
4)
1) Body Homeostasis:
Water metabolism
Temperature regulation
Appetite Control
Sleep-wake cycle and circadian rhythm
Control of SS and PS Nerve Systems

2) Emotional Expression and Behavior

3) Memory

4) Control of Anterior Pituitary Gland
Function
Circadian Rhythm of Cortisol Secretion

What can be determined by measuring the levels of cortisol as given times?
Highest peak of cortisol are measured early in the morning (diagnosis of adrenal insufficiency)
Example: Not enough cortisol = increased ACTH = hyper pigmentation = adrenal insufficiency

Midnight levels of cortisol becomes undetectable (diagnosis of Cushing disease
Regulation of Prolactin Secretion:

1) Increases PRL secretion

2) Decreases PRL secretion
1) Estrogen, breast feedinf, sleep. stress. TRH

2) Dopamine, Bromocriptine, Somatostatin, Prolactin
Patients with primary hypothyroidism can develop ___________.

Explain.
hyperprolactemia

Explaination:
Hypothrodism has low levels of T3 & T4.
Therefore TRH is increased because T3 & T4 are unable to produce a negetive feedback.
TRH casues an increase in prolactin.
Hyperprolactinemia: causes inhibition of pulsatile secretion of GnRH, that leads to:

1) In women

2) In men
1) In women: anovulation, oligomenorrhea or amenorrhea, and infertility.

2) In men: ↓ testosterone synthesis and inhibits spermatogenesis, which clinically is present as decreased libido, impotence, and infertility.
1) Gonadotropin-releasing hormone (GnRH): Binds to receptors on
gonadotrophs and stimulates the secretion of FSH and LH via PLC/IP3
mechanism.

2)Corticotropin-releasing hormone (CRH): Binds to receptors on the
corticotrophs and stimulates ACTH secretion via AC/cAMP.

3) Growth hormone-releasing hormone (GHRH): Binds to receptors on the somatotrophs and stimulates synthesis and release of GH via AC/cAMP.

4)Thyrotropin-releasing hormone (TRH): Binds to receptors on thyrotrophs and stimulates secretion of TSH via PLC/IP3.
Explain.
Hormones
Molecules that transmit endocrine signals
Hormones Can Have Different Functions:
1)
2)
3)
4)
1) Growth and development
2) Maintenance of the internal environment
3) Production, utilization, and storage of energy
4) Reproduction
Ways of Communication of the Endocrine System:

1) Endocrine

2) Paracrine

3) Autocrine

4) Intracrine
1) Endocrine cells secrete hormones which travel through the blood stream to influence target cells that are distributed widely throughout the body.

2) Endocrine cells secrete hormones that act only on cells in the immediate environment.

3) Endocrine cells secrete hormones that act upon the cell that produced it.

Autocrine signals allow the cell to sense and respond to a change in that cell’s environment.

4) A hormone is synthesized and acts intracellularly in the same cell. (Some of the effects of androgen-derived estrogen).
What are the 4 genreal categories that hormones fit into?
1) Protein (polypeptides glycoprotein)
2) Steroids (cholesterol derivatives)
3) Amines (amino acid derivatives)
4) [Eicosanoids] (fatty acids derivatives)
Protein/Peptides Hormones

1) properties

2) biochemical pathway

2) examples
1) Usually water soluble
Not active following oral administration

2) DNA - mRNA - protein
They are synthesized on the polyriobosomes often as a large molecule (prehormones). They then go through shorening steps.

3) Peptides:
Thyrotropin releasing hormone (TRH) Growth hormone (GH) Adrenocorticotropic hormone (ACTH)
Insulin
Glycoprotein Hormones

How many subunits?
What kind?
Do the subuints effect their function?
They are composed of two subunits alpha and β which are non-covalently bound to one another.

Their alpha subunits are identical. It confers species specificity.

Their β subunits are different. It confers distinct immunologic and functional characteristic of the hormones (receptor specificity).

Both subunits are required for full activity.
Cyclopentanoperhydrophenanthrene ring

Steroids
What is this called?

What hormones have this as their backbone?
Steroids are derived from what?

Where does their synthesis occur?

Examples of steroids:
1) Gonadal/Sex steroids

2) Adrenal/Corticosteroids
Cholesterol

Major site of synthesis: adrenal glands, gonads, placenta

Examples of steroids:
1) Gonadal/Sex steroids
Testosterone, Estrogen, Progesterone

2) Adrenal/Corticosteroids
i) Mineralocorticoids: aldosterone

ii) Glucocorticoids: cortisol
Amines
Thyroid hormones:
thyroxine or tetraiodothyronine (T4)
triiodothyronine (T3)

Catecholamines:
epinephrine
nor epinephrine
Eicosanoids
Derive from arachidonic acid (polyunsaturated fatty acids)

Major eicosanoids included: Prostaglandins Leukotrienes
Thromboxanes Prostacyclins

Act as local hormones through G-protein coupled receptors

Interaction between eicosanoids and other hormones

Large spectrum of effects (homeostasis, renal, reproductive, immunological and vascular system, trauma, inflammation, etc.)
Hormone Storage:

1) Protein/peptide hormones

2) Steroid hormones
1) Packaged into secretory vesicles in GolgiStored in secretory vesicles and released by exocytosis.

2) Glandular storage of steroid hormones is minimal. They are fat soluble molecules, able to cross cell membranes relatively easily and therefore they leave the cell rapidly after synthesis.
Key Regulatory Steps

1) If the hormone is stored

2) If the hormone is not stored
1) Proteins/peptide hormones:
If the hormone is stored, then the release of hormone is a key regulatory step. The mechanism usually involves movement of a secretory granule to the cell surface and expulsion of the granule’s contents by exocytosis.

2) Steroids:
If the hormone is not stored, the synthesis is an important regulatory step. The mechanism usually involves an increase in the activity of a key synthetic enzyme or enzyme system by inducing synthesis of the enzyme and/or activating existing enzyme molecules.
The release of hormone is regulated.

Mechanisms regulating hormone release include:

1)

2)

3)
1)Neural control

2) Tropic hormones regulation

3) Feedback mechanisms
Feedback Classification According to the Anatomical Distance:

1) Long loop feedback

2) Short loop feedback

3) Ultra short loop feedback
1) Long loop feedback: Hormones from target glands feedback the hypothalamus or pituitary gland.

2) Short loop feedback: Action of hormones from the pituitary on hypothalamus.

3) Ultra short loop feedback: Pituitary gland or target glands can actually feedback on itself. It is also called auto-regulation
Hormone Transport in Blood:
1) Protein/peptide hormones

2) Steroid hormones
1) Protein/peptide hormones
Soluble in aqueous solvents and, with few exceptions, they circulate in the blood predominantly in an unbound form and therefore tend to have short half life.

2) Steroid hormones
Because of their non-polar nature, they are not readily soluble in blood and therefore are transported mainly bound to plasma proteins.
What is IGF-I?

What does it do?

Where is it made?
Insulin-like growth factor I

A hormone that mediates the action of growth hormone.

Liver and other sources
Mineralcorticoids
They are produced in the zona glomerulosa of the adrenal cortex.

Act mainly on the kidneys to control electrolyte balance.

Aldosterone - promotes Na+ retention & K+ excretion by the kidneys.
Glucocorticoids
They are produced in the zona fasciculata of the adrenal cortex.

Cortisol
True/False

The gonads are both exocrine and endocrine?
True

Endocrine = gonadal hormones

Exocrine = eggs & sperm
Which hormones act using the AC/cAMP mechanism?
ACTH
LH
FSH

note:
AC = adenylate cyclase
Which hormones act using the DAG and IP3 mechanism?
ADH
TRH
OT

note:
DAG = Diacylglycerol
IP3 = Inositol triphosphate
Define:

1) Up regulation

2)Down regulation
1) a cell increases the number of hormone receptors and becomes more sensitive to the hormone.
Example - oxytocin

2) a cell reduces its receptor populaiton & thus becomes less sensitive to a hormone.
Stress causes a rise in what hormones?
Glucocorticoids, especially Cortisol
Cortisol
stimulates gastric secretion, which may aggravate the ulcers that occur in chronic stress.

Coritisol suppresses the secretion of LH, testosterone, estrogen
1) Antagonist
1) any hormone that opposes another