ENDOCRINE SYSTEM Flashcards
Hormones are classified chemically as:
•Amino acid–based, which includes:
▪ Proteins
▪ Peptides
▪ Amines
•Steroids—made from cholesterol
•Prostaglandins—made from highly active lipids that act
as local hormones
Hormones act by two mechanisms
- Direct geneactivation
▪ Used by steroid hormones and thyroid hormone - Second-messengersystem
▪ Used by protein and peptide hormones
what is the
activation is
- Steroid hormones diffuse through the plasma
membrane of target cells - Once inside the cell, the hormone enters the nucleus
- Then, the hormone binds to a specific protein within the nucleus
- Hormone-receptor complex binds to specific sites on the cell’s DNA
- Certain genes are activated to transcribe messenger RNA
- New proteins are synthesized
▪Direct gene activation
WHAT TYPE OF ACTIVATION
- Hormone (first messenger) binds to a membrane
receptor - Activated receptor sets off a series of reactions that activates an enzyme
- Enzyme catalyzes a reaction that produces a second-messenger molecule (such as cyclic AMP, known as cAMP)
- Oversees additional intracellular changes to promote a specific response in the target cell
Second Messenger System
The stimuli that activate endocrine glands fall into three major categories
- Hormonal 2. Humoral 3. Neural
▪ Most common category of stimulus
▪ Endocrine organs are activated by other hormones
Example:
▪ Hormones of the hypothalamus stimulate the anterior pituitary to secrete its hormones
Hormonal stimuli
▪ Changing blood levels of certain ions and nutrients
stimulate hormone release
▪ Humoral indicates various body fluids, such as blood and bile
Examples:
▪ Parathyroid hormone and calcitonin are produced in
response to changing levels of blood calcium levels
▪ Insulin is produced in response to changing levels of blood glucose levels
Humoral stimuli
▪ Nerve fibers stimulate hormone release
▪ Most are under the control of the sympathetic nervous system
▪ Examples:
▪ Sympathetic stimulation of the adrenal medulla to
release epinephrine and norepinephrine
Neural stimuli
The Major Endocrine Organs
▪ Hypothalamus
▪Pituitary gland
▪Pineal gland
▪Thyroid gland
▪Parathyroid glands
▪ Thymus
▪Adrenal glands
▪ Pancreas
▪Gonads (testes and ovaries)
Some glands have purely endocrine functions
▪ Anterior pituitary, thyroid, adrenals, parathyroids
Other glands are mixed glands, with both endocrine and exocrine functions
(pancreas, gonads)
▪ Pea-sized gland that hangs by a stalk from the
hypothalamus in the brain
▪ Protected by the sella turcica of the sphenoid bone
▪ Has two functional lobes
▪ Anterior pituitary—glandular tissue ▪ Posterior pituitary—nervous tissue
▪ Often called the “master endocrine gland”
Pituitary gland
Hypothalamus also makes two hormones:
oxytocin and antidiuretic hormone
▪ Carried to posterior pituitary via neurosecretory cells for storage
▪ Does not make the hormones it releases
▪ Stores hormones made by the hypothalamus
▪Two hormones released ▪ Oxytocin
▪ Antidiuretic hormone (ADH)
Posterior pituitary
WHAT HORMONE?
▪ Stimulates contractions of the uterus during labor, sexual relations, and breastfeeding
▪ Causes milk ejection (let-down reflex) in a breastfeeding woman
▪ Oxytocin
WHAT HORMONE
▪ Inhibits urine production (diuresis) by promoting water reabsorption by the kidneys
▪ Urine volume decreases, blood pressure increases
▪ In large amounts, causes constriction of arterioles, leading to increased blood pressure (the reason why ADH is known as vasopressin)
▪ Alcohol inhibits ADH secretion
(Posterior pituitary )
Antidiuretic hormone (ADH)
Six anterior pituitary hormones
▪ Two hormones affect nonendocrine targets
1. Growth hormone
2. Prolactin
▪ Four are tropic hormones
1. Follicle-stimulating hormone
2. Luteinizing hormone
3. Thyrotropic hormone
4. Adrenocorticotropic hormone
Six anterior pituitary hormones
▪ Two hormones affect nonendocrine targets
1. Growth hormone
2. Prolactin
▪ Four are tropic hormones
1. Follicle-stimulating hormone
2. Luteinizing hormone
3. Thyrotropic hormone
4. Adrenocorticotropic hormone
All anterior pituitary hormones: ARE?
▪ Are proteins (or peptides)
▪ Act through second-messenger systems
▪ Are regulated by hormonal stimuli
▪ Are regulated mostly by negative feedback
WHAT HORMONE
▪ General metabolic hormone
▪ Major effects are directed to growth of skeletal muscles and long bones
▪ Plays a role in determining final body size
▪ Causes amino acids to be built into proteins
▪ Causes fats to be broken down for a source of energy
Growth hormone (GH)
PITUITARY GLAND & HYPOTHALAMUS
WHAT HORMONE?
Stimulates and maintains milk production following
childbirth
▪ Function in males is unknown
Prolactin (PRL)
PITUITARY GLAND & HYPOTHALAMUS
WHAT HORMONE?
▪ Regulate hormonal activity of the gonads
▪ Follicle-stimulating hormone (FSH)
▪ Stimulates follicle development in ovaries ▪ Stimulates sperm development in testes
▪ Luteinizing hormone (LH)
▪ Triggers ovulation of an egg in females
▪ Stimulates testosterone production in males
Gonadotropic hormones
PITUITARY GLAND & HYPOTHALAMUS
WHAT HORMONE?
Influences growth and activity of the thyroid gland
▪Thyrotropic hormone (TH), also called thyroid- stimulating hormone (TSH)
PITUITARY GLAND & HYPOTHALAMUS
▪ Regulates endocrine activity of the adrenal cortex
Adrenocorticotropic hormone (ACTH)
PITUITARY GLAND & HYPOTHALAMUS
WHAT GLAND
Hangs from the roof of the third ventricle of the brain
▪Secretes melatonin
▪ Believed to trigger the body’s sleep/wake cycle
▪ Believed to coordinate the hormones of fertility in humans and to inhibit the reproductive system until maturity occurs
PINEAL GLAND
WHAT GLAND
▪Found at the base of the throat, inferior to the Adam’s apple
▪Consists of two lobes and a connecting isthmus
▪Follicles are hollow structures that store colloidal
material
▪Produces two hormones 1. Thyroidhormone
2. Calcitonin
Thyroid Gland
WHAT HORMONE
▪ Major metabolic hormone
▪ Controls rate of oxidation of glucose to supply body heat and chemical energy
▪ Needed for tissue growth and development
▪ Composed of two active iodine-containing hormones
▪ Thyroxine (T4)—secreted by thyroid follicles
▪ Triiodothyronine (T3)—conversion of T4 at target tissues
Thyroid hormone
Thyroid Gland
WHAT HORMONE
▪ Decreases blood calcium levels by causing calcium
deposition on bone
▪ Antagonistic to parathyroid hormone
▪ Produced by parafollicular cells found between the follicles
Calcitonin
Thyroid Gland
WHAT GLAND
▪Tiny masses on the posterior of the thyroid ▪Secrete parathyroid hormone (PTH)
▪ Most important regulator of calcium ion (Ca2+) homeostasis of the blood
▪ Stimulates osteoclasts to remove calcium from bone ▪ Hypercalcemic hormone (increases blood calcium
levels)
▪ Stimulates the kidneys and intestine to absorb more calcium
Parathyroid Glands
WHAT GLAND
▪Located in the upper thorax, posterior to the sternum
▪Largest in infants and children
▪Decreases in size throughout adulthood
▪Produces a hormone called thymosin
▪ Matures some types of white blood cells
▪ Important in developing the immune system
Thymus
WHAT GLAND
▪Sit on top of the kidneys ▪Two regions
1. Adrenal cortex—outer glandular region has three layers that produce corticosteroids
▪ Mineralocorticoids are secreted by outermost layer
▪ Glucocorticoids are secreted by middle layer
▪ Sex hormones are secreted by innermost layer
2. Adrenalmedulla—inner neural tissue region
Adrenal Glands
WHAT GLAND
▪ Mineralocorticoids (mainly aldosterone)
▪ Produced in outer adrenal cortex
▪ Regulate mineral (salt) content in blood, particularly sodium and potassium ions
▪ Regulate water and electrolyte balance ▪ Target organ is the kidney
▪Hormones of the adrenal cortex
Adrenal Glands
WHAT GLAND
▪Hormones of the adrenal cortex (continued) ▪ Release of aldosterone is stimulated by:
▪ Humoral factors (fewer sodium ions or too many potassium ions in the blood)
▪ Hormonal stimulation (ACTH)
▪ Renin and angiotensin II in response to a drop in blood
pressure
▪ Aldosterone production is inhibited by atrial natriuretic peptide (ANP), a hormone produced by the heart when blood pressure is too high
Adrenal Glands
WHAT GLAND
▪ Glucocorticoids (including cortisone and cortisol)
▪ Produced by middle layer of adrenal cortex
▪ Promote normal cell metabolism
▪ Help resist long-term stressors by increasing blood glucose levels (hyperglycemic hormone)
▪ Anti-inflammatory properties
▪ Released in response to increased blood levels of
ACTH
Hormones of the adrenal cortex (continued)
ADRENAL GLANDS
)WHAT GLAND
▪ Sex hormones
▪ Produced in the inner layer of the adrenal cortex ▪ Small amounts are made throughout life
▪ Most of the hormones produced are androgens (male sex hormones), but some estrogens (female sex hormones) are also formed
▪Hormones of the adrenal cortex (continued)
ADRENAL GLANDS
WHAT GLAND
▪ Produces two similar hormones (catecholamines)
1. Epinephrine (adrenaline)
2. Norepinephrine (noradrenaline)
▪ These hormones prepare the body to deal with short- term stress (“fight or flight”) by:
▪ Increasing heart rate, blood pressure, blood glucose levels
▪ Dilating small passageways of lungs
▪Adrenal medulla
Adrenal Glands
WHAT GLAND
▪ Located in the abdomen, close to stomach
▪ Mixed gland, with both endocrine and exocrine functions
▪The pancreatic islets (islets of Langerhans) produce hormones
▪ Insulin—produced by beta cells
▪ Glucagon—produced by alpha cells
▪ These hormones are antagonists that maintain blood sugar homeostasis
▪ Pancreas
Pancreatic Islets
WHAT HORMONE
▪ Released when blood glucose levels are high
▪ Increases the rate of glucose uptake and metabolism by body cells
▪ Effects are hypoglycemic
▪ Insulin
Pancreatic Islets
WHAT HORMONE
▪ Released when blood glucose levels are low
▪ Stimulates the liver to release glucose to blood, thus increasing blood glucose levels
Glucagon
Pancreas Islets
WHAT GLAND
▪ Produce sex cells
▪ Produce sex hormones
▪ Gonads
▪ Female gonads located in the pelvic cavity
▪ Produce eggs
▪ Produce two groups of steroid hormones 1. Estrogens
2. Progesterone
▪ Ovaries
Gonads
▪ Male gonads suspended outside the pelvic cavity
▪ Produce sperm
▪ Produce androgens, such as testosterone
Testes
Gonads
WHAT HORMONE
▪ Stimulate the development of secondary female
characteristics
▪ Mature the female reproductive organs
▪With progesterone, estrogens also: ▪ Promote breast development
▪ Regulate menstrual cycle
Estrogens
WHAT HORMONE
▪ Acts with estrogen to bring about the menstrual cycle
▪ Helps in the implantation of an embryo in the uterus ▪ Helps prepare breasts for lactation
Progesterone
GONADS
▪Produce several androgens
▪Testosterone is the most important androgen
▪ Responsible for adult male secondary sex characteristics
▪ Promotes growth and maturation of male reproductive system
▪ Required for sperm cell production
Testes
GONADS
Other organs that are generally nonendocrine in function also secrete hormones
▪ Stomach ▪Small intestine ▪ Kidneys
▪ Heart
▪ Produces hormones that maintain pregnancy
▪ Some hormones play a part in the delivery of the baby
▪ Produces human chorionic gonadotropin (hCG) in addition to estrogen, progesterone, and other hormones
▪ Human placental lactogen (hPL) prepares the breasts for lactation
▪ Relaxin relaxes pelvic ligaments and pubic symphysis for childbirth
Placenta
▪Efficiency of all endocrine glands gradually decreases with aging, which leads to a generalized increase in incidence of:
▪ Diabetes mellitus
▪ Immune system depression ▪ Lower metabolic rate
▪ Cancer rates in some areas
