BN Ch.20 The Endocrine System Flashcards
1
Q
Differentiate between exocrine and endocrine glands.
A
- Endocrine glands secrete hormones directly into the bloodstream
- Exocrine glands secrete hormones into ducts.
- Exocrine glands secrete special substances (hormones and/or other materials) into ducts that open onto the body’s external or internal surfaces.
- Exocrine glands include sweat, mammary, and salivary glands, as well as mucous membranes and lacrimal (tear) glands.
- Examples of exocrine secretions are
- sweat
- milk
- bile
- tears
- pancreatic fluid.
- Endocrine glands ( ductless glands , glands of internal secretion) secrete hormones directly into the bloodstream, where they are transported throughout the body.
- These hormones act on remote tissues ( target tissues ) via endocrine signaling .
- Certain glands can perform both endocrine and exocrine functions.
2
Q
Describe the general functions of the endocrine system and the actions related to each.
A
- Growth and Maturation
- Regulates growth and maturation
- Regulates body’s response to stress
- Metabolism
- Regulates metabolism
- Regulates absorption of nutrients
- Regulates use of glucose in cellular respiration
- Maintains body pH by maintaining fluid and electrolyte concentrations
- Reproduction
- Produces sexual characteristics
- Controls reproductive and birth processes
- Promotes normal growth and development
- Activates lactation
- Influences sexual response
3
Q
Describe the relationship between the hypothalamus and the pituitary gland.
A
Many hormones are secreted in the hypothalamus; they, in turn, control the release of hormones by the pituitary.
4
Q
Identify major hormones released by the anterior, middle, and posterior divisions of the pituitary; describe the functions of each.
A
Anterior Lobe:
- Prolactin (lactogenic hormone) (PRL)
- Stimulated by PRH from hypothalamus LH (in males)
- Stimulates mammary glands to produce milk (after pregnancy); influences sexual gratification
- Growth hormone (GH or hGH)
- Controls bone and tissue growth and regulates metabolism (influences secretion of insulin-like growth factor I from liver)
- somatotropic hormone—stimulated by GRH, GHRH from hypothalamus is another name for Growth hormone.
- Adrenocorticotropic hormone (ACTH, corticotropin)
- Stimulated by CRH from hypothalamus
- Stimulates adrenal cortex to produce cortisol, corticosteroids, and androgens; can stimulate melanocytes
- Luteinizing hormone (LH) (in females)
- Helps control ovulation and menstruation
- important in sustaining pregnancy
- Follicle-stimulating hormone (FSH)—stimulated by GnRH
- Stimulates growth and secretion of eggs in ovaries (female) and sperm in testes (male)
- Thyroid-stimulating hormone (TSH)
- stimulated by TRH from hypothalamus
- Regulates thyroid hormone (via secretion of thyroxine [T 4] and triiodothyronine [T 3])
Middle:
- Melanocyte-stimulating hormone (MSH)
- stimulated by CRH from hypothalamus
- Increases skin and hair pigmentation
Posterior Lobe: (neurohypophysis)
- Stores hormones only—no production
- Oxytocin
- Causes uterine contractions; contractions of cervix and vagina; influences orgasm; stimulates milk production;
- Vasopressin
- (antidiuretic hormone—ADH)
- Raises blood pressure (some vasoconstriction)
- Promotes water reabsorption in kidney tubules
- Influences uterus
5
Q
Describe the actions of hormones responsible for calcium balance.
A
- Calcitonin ( CT ) or thyrocalcitonin
- CT (and parathyroid hormone) are involved in the maintenance of calcium levels.
- When the circulating calcium level is high, calcitonin responds by promoting increased storage of calcium in bones and increased renal excretion of calcium, resulting in lowered serum calcium.
- Parathormone or parathyroid hormone ( PTH )
- That regulates the amounts of calcium and phosphorus in the blood, which in turn affects nerve and muscle irritability.
- When the blood calcium level is too low, PTH is secreted, increasing the number and size of osteoclasts (large cells associated with reabsorption of bone).
- Therefore, PTH causes calcium to leave the bones and also enhances reabsorption of calcium and magnesium and excretion of phosphorus in the kidneys.
- PTH also affects the kidneys by promoting calcitriol formation.
- This is a hormone synthesized from vitamin D, which increases the rate of calcium, magnesium, and phosphorus absorption from the gastrointestinal tract into the blood.
6
Q
Describe the relationships between “releasing” hormones and “inhibiting” hormones.
A
- Releasing hormones and inhibiting hormones are hormones whose main purpose is to control the release of other hormones, either by stimulating or inhibiting their release.
- Specialized cells in the hypothalamus release hormones that either inhibit or promote release of other hormones from the anterior lobe of the pituitary.
7
Q
Describe the hormones involved in “fight or flight”; give examples of their effects and body’s responses during an emergency.
A
- Epinephrine (adrenaline) constitutes about 80% of the medullas total secretion and is important in managing and adapting to stress.
- Epinephrine causes an increase in pulse rate, blood vessel contraction, a rise in blood pressure, and increased muscle power, by causing the liver to release glucose for energy.
- The hormone norepinephrine has some—but not all—actions of epinephrine.
- These two hormones mimic the action of the sympathetic nervous system and are active in:
- Emergencies
- Fright, anger, love, and grief stimulate them.
- They are said to enable “fight or flight” reactions.
- If the adrenal medulla is absent, the sympathetic nervous system can take over its activities.
- These two hormones mimic the action of the sympathetic nervous system and are active in:
8
Q
Explain the functions of the thyroid hormones.
A
- The epithelial cells of the thyroid synthesize two hormones:
- Thyroxine (Tetraiodothyronine or T4)
- Triiodothyronine (T3) from the iodine.
- T4 is the less potent form of thyroid hormone.
- More T4 (90%) is found in the blood, compared with T3 .
- It is believed that T4 is converted to T3 before it is effective.
- Thyroid hormones regulate body metabolism, controlling the rate at which cells function.
- Protein synthesis relies on these hormones, and they also affect sensitivity to catecholamines (important in stress responses) and sympathetic amines (e.g., dopamine and epinephrine).
- Because the thyroid requires iodine to form T4 , a person’s diet must supply iodine.
9
Q
Describe the functions of mineralocorticoids and glucocorticoids secreted by the adrenals.
A
- Mineralocorticoids
- Regulate the body’s electrolytes.
- Aldosterone, the most important mineralocorticoid, stimulates reabsorption of sodium into plasma and secretion of potassium and hydrogen in the kidney, resulting in increased water reabsorption and, therefore, an increase in blood volume.
- Glucocorticoids
- Have an important influence on the synthesis of glucose, amino acids, and fats during metabolism.
- They also depress the immune response, decrease the inflammatory response, and contribute to the maintenance of normal blood pressure.
- Corticosteroid production is normally increased during stress.
- Hydrocortisone (cortisol) is the predominant glucocorticoid.
10
Q
Discuss the role of the thymus as an endocrine organ and its relationship to the body’s immune response.
A
As an endocrine organ:
- Thymus consists of lymphatic tissue and lies behind the sternum (breast bone).
- It also consists of an outer cortex and inner medulla.
- The thymus is the lymphatic system’s primary controlling gland.
- It produces thymosin (thymic hormone), a protein that promotes growth of lymphatic tissue, and a naturally occurring immunologic hormone, thymopoietin.
Relationship to bodies immune system:
- Thymosin stimulates production of small lymphocytes called T-cells (also called T lymphocytes, T-helper cells , or thymus-dependent cells ) and also secretes other hormones believed to assist in maturation of T-cells.
- T-cells are essential for the development of cellular immunity and the body’s response to invading organisms.
- If a person’s T-cell count is diminished, that person would have difficulty fighting off attacking pathogens.
11
Q
Briefly identify male and female sex hormones and functions of each.
A
- Androgen (testosterone, male)
- the Leydig cells of the testes produce testosterone, the male sex hormone.
- Develops male sex characteristics (also influenced by androgens) produce masculinizing effects.
- Estrogen (dehydroepiandrosterone [DHEA], female).
- The female ovaries produce estrogen (primarily estradion) and progesterone, which, in addition to regulating female sex characteristics, are responsible for menstruation;
- They also influence pregnancy, labor, and lactation.
- In addition, progesterone has an influence on many body functions, including blood clotting, thyroid and nerve function, and the gallbladder.
12
Q
Discuss negative and positive feedback as they relate to the endocrine system.
A
- The fine balance within the endocrine system called feedback regulates the rate and quantity of hormone secretion.
- Negative feedback signals the controller (the specific gland) to correct a deviation from normal.
- Negative feedback receptors (e.g., glands) require close monitoring by body cells in order to maintain the desired hormone level.
- After the desired effect is achieved, information is sent to the gland to halt hormonal secretion.
- This is a negative feedback system or loop , because the body has again achieved homeostasis.
- This situation will now cause an inhibited glandular response.
- An example is the secretion of insulin to correct the situation of excess blood sugar.
- A positive feedback system or loop can also occur.
- For example, if a hormone is needed to meet the body’s needs, a message is carried to the appropriate gland (as in the negative feedback system).
- The result is increased hormone production.
- Hormone secretion does not cease (as in negative feedback), but instead continues and intensifies.
- An example of a positive feedback system is the hormone oxytocin, produced during labor.
- Oxytocin intensifies uterine contractions and enables the uterus to expel the fetus.
- The goal of feedback systems in the body is to help promote homeostasis
- The basic mechanisms controlling hormonal release include stimulation by other hormones, chemical signals, and nerve stimulation.
13
Q
Explain the role of prostaglandins.
A
- Prostaglandins are hormone-like substances.
- The three most common prostaglandins are:
- Prostaglandins A (PGA)
- Prostaglandins E (PGE)
- Prostaglandins F (PGF)
- They can cause pain, perform a role in platelet function, and stimulate either contraction or relaxation in smooth muscle.
- The prostaglandins influence:
- Blood pressure
- Respiration
- Digestion
- Reproduction
- Inflammatory responses
- In some cases actually can have opposite effects on these functions.
14
Q
Describe four effects of aging on the endocrine system.
A
-
Reproductive hormones decrease
- Onset of menopause in middle age
- Sexual organs shrink;
- Women lose ability to become pregnant
- Hirsutism in women
- Atrophy of subcutaneous breast tissue;
- fat replaces glandular tissue;
- breasts sag
- Decreased sperm production;
- Impotence may occur (but is not universal)
-
Sexual tissue atrophies
- Loss of pubic hair
- Longer time needed for sexual orgasm
- Lessened amount of vaginal secretion
-
Decrease in thyroid hormones
- Decreased metabolic clearance rate
- Thinning hair;
- Male pattern baldness
- Dry skin
-
Decrease in pancreatic secretions
- Decreased ability to metabolize glucose
15
Q
Name the hormones secreted by non endocrine glands or organs; state the function of each.
A
- Atrial-natriuretic peptide (ANP), atrial-natriuretic factor (ANf)
- Reduces blood pressure by decreasing vascular resistance and fluid volume; influences balance of sodium and fats in blood
- Brain-natriuretic peptide (BNP)
- Influences lowering of blood pressure
- Thrombopoietin
- Stimulates platelet production
- Insulin-like growth factor (somatomedin)
- Regulates cell growth and development;
- also has insulin-like effects
- Angiotensin and angiotensinogen
- Vasoconstriction; influence release of aldosterone from adrenal cortex
- Renin
- Activates renin-angiotensin system by stimulating production of angiotensin I and angiotensinogen
- Erythropoietin (EPO)
- Stimulates production of erythrocytes (red blood cells [RBCs])
- Calcitriol
- Increases calcium and phosphate absorption, inhibits release of parathyroid hormone (PTH)
- Gastrin and histamine
- Stimulate secretion of gastric acid
- Ghrelin
- Secreted by cells in stomach lining—slows metabolism and fat burning, may contribute to obesity; stimulates appetite; stimulates secretion of GH
- Leptin
- Secreted by fat-storing cells—regulates hunger and fat metabolism
- Neuropeptide Y (NPY)
- Increases food intake; decreases physical activity; decreases secretion of bicarbonate
- Secretin and pancreozymin
- Enhance effects of cholecystokinin (CCK);
- Stop production of gastric juice
- Stimulate pancreas to release pancreatic juice.
- Stimulate secretion of bicarbonate from liver, pancreas, and duodenum (Brunner glands)
- Somatostatin
- Suppresses release of gastrin, cholecystokinin (CCK), secretin, and other substances; reduces rate of gastric emptying; reduces smooth muscle contractions and intestinal blood flow
- Histamine
- Stimulates gastric acid secretion
- Endothelin
- Influences smooth muscle contractions in stomach
- Cholecystokinin (CCK)
- Stimulates release of digestive enzymes from pancreas, release of bile from gallbladder; suppresses hunger
- Human incretin hormone (glucagon-like peptide-I)
- Influences secretion of insulin by pancreas
