Ch. 11 Endocrine Glands Flashcards
Homeostatic effectors are controlled by which gland: endocrine or exocrine?
Endocrine glands
Endocrine Glands
Secrete hormones into blood
Hormones are carried to Target Cells which have receptors for those hormones
Many organs secrete hormones. List 4.
- Heart
- Liver
- Kidneys
- Adipose tissue
Hormone signaling involves a lot of different organs
Neurohormones
Secreted by specialized cells of the hypothalamus
Hormones help regulate many different things. List 3.
- Body metabolism
- Growth
- Reproduction
Chemical Classification of Hormones: Amines
Derived from tyrosine and tryptophan
ex: hormones from adrenal medulla, thyroid, and pineal glands
Chemical Classification of Hormones: Polypeptides and Proteins
ex: antidiuretic hormone, insulin, and growth hormone
Chemical Classification of Hormones: Glycoproteins
Long polypeptides bound to a carbohydrate
ex: follicle-stimulating and luteinizing hormones
Chemical Classification of Hormones: Steroids
Lipids derived from cholesterol (not very water-soluble)
ex: testosterone, estradiol, progesterone, cortisol
Secreted by adrenal cortex and gonads
Synergistic Effects
Occur when 2 or more hormones work together to produce a particular effect
Synergistic Effects: Additive
Epinephrine and norepinephrine each affect the heart in the same way
Even if you take epinephrine away, norepinephrine is still affecting the organ in the same way
Synergistic Effects: Complementary
Each hormone contributes a different piece of an overall outcome
–ex: producing milk requires estrogen, prolactin, and oxytocin
Permissive Effects
Subset of complementary effect
Occur when one hormone makes the target cell more responsive to a second hormone
Exposure to estrogen makes the uterus more responsive to progesterone
–estrogen sets stage for effects of progesterone
Increased secretion of PTH makes intestines more responsive to Vitamin D3 in calcium absorption
How do permissive effects work?
First hormone –> sensitizes organ to effects of 2nd hormone –> get desired effects from 2nd hormone (2nd hormone is actually inducing effect)
Antagonistic Effects
Occur when hormones work in opposite directions
Insulin and glucagon both affect adipose tissue
- -insulin stimulates fat storage
- -glucagon stimulates fat breakdown
Have to be working on same organ to be antagonistic effects
Hormone Action
Hormones bind to receptors on or in target cells
- -binding is highly specific
- -hormones bind to receptors w/ a High Affinity
- -hormones bind to receptors w/ a low capacity; saturating the receptors w/ hormone molecules
Hormones are released at really low doses
Hormone Action: Lipophilic hormone receptors
In cytoplasm or nucleus
Hydrophobic, receptors found inside cell
Hormone Action: Water-soluble hormone receptors
On outer surface of plasma membrane
Facing eternal environment
Nuclear Receptors
Lipophilic steroid hormones and thyroid hormone
- -travel to target cells attached to Carrier Proteins
- -at the target cell, dissociate from the carrier protein and diffuse across the plasma membrane
- -receptors are found w/in the nucleus and are called Nuclear Hormone Receptors because they activate genetic transcription
These hormone receptors serve as Transcription Factors
–making mRNA
They are activated by the binding of the hormone
The effect of these hormones is therefore to produce new proteins, usually enzymes that change metabolism inside the cell
Going to affect gene expression
Hormones: 2nd Messengers
Hormones that cannot cross the plasma membrane
–water-soluble
Activate an intracellular mediator called a 2nd Messenger
List the 3 major 2nd messenger mechanisms
- Adenylate cyclase (activates a protein kinase)
- Phospholipase C (controls intracellular Ca2+)
- Tyrosine kinases
Pituitary gland is attached to the hypothalamus by the ____.
Infundibulum
The pituitary gland is divide into what lobes?
Anterior lobe (adenohypophysis)
Posterior lobe (neurohypophysis)
Anterior Pituitary
Glandular epithelium w/ 2 parts - pars distalis and pars tuberalis
Posterior Pituitary
Nervous tissue
aka pars nervosa
Anterior Pituitary Hormones
Trophic hormones stimulate hormone secretion in other glands:
- -growth hormone (GH)
- -thyroid-stimulating hormone (TSH)
- -adrenocorticotropic hormone (ACTH)
- -follicle-stimuatling hormone (FSH)
- -luteinizing hormone (LH) - in the male, it is interstitial cell stimulating hormone (ICSH)
- -prolactin (PRL)
Feedback Control of the Anterior Pituitary
Final product regulate secretion of pituitary hormones - negative feedback inhibition
Relationship between the hypothalamus, anterior pituitary, and target tissue is called an Axis
Inhibition can occur at the pituitary gland level, inhibiting response to hypothalamic hormones
Inhibition can occur at the hypothalamus level, inhibiting secretion of releasing hormones
Posterior Pituitary Hormones
Stores and releases 2 hormones made in hypothalamus
- -Antidiuretic Hormone (ADH): promotes retention of water in kidneys (also called arginine vasopressin - AVP)
- -Oxytocin: stimulates contractions in childbirth and milk let-down in lactation
Adrenal Glands
Found atop the kidneys
Consist of an outer adrenal cortex and an inner adrenal medulla that function as 2 separate glands
–one organ, 2 real parts
Adrenal Glands: Adrenal Medulla
Adrenal Medulla is neural tissue and secretes epinephrine and norepinephrine in response to sympathetic neural stimulation
Adrenal Glands: Adrenal Cortex
Adrenal Cortex is glandular epithelium and secretes steroid hormones in response to ACTH (comes from anterior pituitary gland)
3 layers:
- -zona glomerulosa
- -zona fasciculata
- -zona reticularis
Adrenal Cortex
Secretes hormones made from cholesterol; called corticosteroids or corticoids
3 categories:
- -Mineralocorticoids
- -Glucocorticoids
- -Adrenal androgens
Mineralocorticoids
From zona glomerulosa
Regulate Na+ and K+ balance
ex: Aldosterone
Glucocorticoids
From zona fasciculata
Regulate glucose metabolism
ex: Cortisol
Adrenal Androgens
From zona reticularis
Weak sex hormones that supplement those made in the gonads
Cortisol (Hydrocortisone)
Stimulates protein degradation
–allows us to get energy from protein
Stimulates gluconeogenesis (making glucose) and inhibits glucose utilization to raise blood glucose levels
Stimulates lipolysis
When do cortisol levels spike?
Early in the day
When stressed
Thyroid Gland
Located just below the larynx
Has 2 lobes on either side of the trachea, connected by the isthmus
Thyroid Gland Structure
Consists of hollow spaces called Thyroid Follicles lined w/ simple cuboidal epithelium composed of Follicular Cells that produce Thyroglobulin
Interior of the follicles is filled w/ a fluid called Colloid
Outside of the follicles are Parafollicular Cells that secrete Calcitonin
Production of Thyroid Hormone
Thyroglobulin is made by follicular cells
Thyroid follicles actively accumulate Iodide (I-) and secrete it into the colloid.
- -iodine is attached to tyrosines w/ the thyroglobulin molecule
- -1 iodine produces monoiodotyrosine (MIT)
- -2 iodines produce diiodotyrosine (DIT)
Enzyme w/in the colloid attach MIT and DIT together:
- -DIT + DIT = T4 (thyroxine)
- -DIT + MIT = T3 (triiodothyronine)
These are still bound to thyroglobulin
- -dissociate from thyroglobulin when the thyroid gland is stipulated by TSH
- -secreted into the blood
What is T4?
Thyroxine
DIT + DIT = T4
What is T3?
Triiodothyronine
DIT + MIT =T3
T3/T4: Which one is the active form? Which one can be converted to the other by iodinases?
T3 is active form
T4 (longer half-life) can be converted by T3 by iodinases in cells
Thyroid Hormone
- Stimulates protein synthesis
- Promotes maturation of nervous system
- Increases rates of cellular respiration
- Elevates basal metabolic rate
What are 2 diseases associated w/ thyroid problems?
Hyperthyroidism and Hypothyroidism
Parathyroid Gland
Generally 4 glands embedded in the back of thyroid gland
Secrete Parathyroid Hormone (PTH)
Hormone promotes a rise in blood calcium by acting on bones, kidneys, and intestines
–PTH tells kidneys to retain calcium, tells bones to break down a little to get more calcium, and tells intestines to absorb more calcium
Pancreas
Both an endocrine and exocrine gland
Endocrine cells are located in pancreatic islets (islets of Langerhans)
Pancreas: Alpha Cells
Glucagon
Pancreas: Beta Cells
Insulin
destruction of Beta cells = type 1 diabetes
Insulin
Primary hormone regulating plasma glucose concentration
Secreted by beta cells when blood glucose levels rise after a sugary or CHO meal
Its purpose is to lower blood glucose levels to the “normal’ range
Insulin: Mechanisms of Work
Binds to receptors on target cells
- -vesicles w/ GLUT4 carrier proteins bind to membrane
- -glucose diffuses through GLUT4 channels by facilitated diffusion
- -occurs in adipose tissue, skeletal muscle, and the liver
Indirectly stimulates the enzyme glycogen synthase in liver and skeletal muscles to promote sugar storage
Stimulates adipose tissue to store fat
How soon does the body to store blood glucose after eating?
W/in minutes in ingesting a meal
Glucagon
Antagonistic to insulin
Secreted by alpha cells when blood glucose levels are low
Purpose is to raise blood glucose levels to a “normal” level
Stimulates liver to hydrolyze glucagon into glucose (glycogenolysis) and release it into the blood
Stimulates gluconeogenesis, conversion of nonCHOs into glucose
Stimulates lipolysis in adipose tissue so fat is released as used as a fuel source instead of glucose
