The Endocrine and Excretory System

Question 1

state the principal differences between the endocrine and nervous systems.

Answer 1

nervous:

• rapid response
• uses electrochemical impulses and neurotransmitters
• mainly affects muscle fibres, smooth muscle (in blood vessel and organs), and glands

endocrine:

• usually slower, more prolonged response though exceptions exist - e.g. adrenalin and cortisol are released rapidly
• uses chemical messengers or hormones
• affects most body cells

Question 2

describe exocrine glands.

Answer 2

secrete their products into ducts - hormones

these glands include sweat glands, sebaceous glands, mucous glands, digestive glands

Question 3

describe endocrine glands.

Answer 3

secrete hormones into the blood

• hormones diffuse into the blood stream through capillaries and are carried to target cells throughout the body
• primary endocrine tissue includes hypothalamus, pituitary, thyroid, parathyroid glands, adrenal glands etc.

Question 4

what are hormones, and what effect do they have on cells?

Answer 4

a diverse group of chemical substances that act on specific target cells.
- hormones travelling throughout the body will only affect target cells that possess specific protein receptors

Question 5

what is the difference between water-soluble hormones and lipid-soluble hormones?

Answer 5

water-soluble: circulate freely in the plasma

lipid-soluble: circulate bound to transport proteins

Question 6

state some responses target cells may have due to hormones.

Answer 6

• changes in the expression of particular genes
• changing permeability of cell membrane
• causing contraction of smooth or cardiac muscle

Question 7

state some factors that influence the way a target cell responds to a hormone.

Answer 7

• the hormones concentration in the blood
• the number of hormone receptors on the target cell
• influences exerted by other hormones

Question 8

how is hormone secretion regulated?

Answer 8

• signals from the nervous system
• activation of chemoreceptors
• chemical changes in the blood
• other hormones

MOST hormone regulation is achieved via negative feedback, however a few operate via positive feedback (e.g. oxytocin)

Question 9

explain the mechanisms of hormone action

Answer 9

water-soluble hormones bind to receptors on the exterior surface of the target cell.
lipid-soluble hormones bind to receptors within target cells.

Question 10

describe how protein hormones exert their effect on target cells.

Answer 10

water-soluble and therefore cannot directly pass through plasma membrane of target cell.
bind to receptors on plasma membrane casing structural change in the cell membrane and the activation of intracellular second messengers which exert changes

Question 11

which organs synthesise and release steroid hormones? what type of hormones does it release?

Answer 11

the adrenal cortex and the gonads

release from adrenal cortex:

• glucocorticoids such as cortisol
• mineralocorticoids such as aldosterone
• gonadocorticoids such as weak androgens. androgens are converted to testosterone and oestrogen

release from gonads:

• testosterone
• oestrogen and progesterone

Question 12

explain the term ‘tropic hormone’ and list the four tropic hormones produced by the anterior pituitary

Answer 12

tropic hormone - hormone that is produced in one endocrine gland and regulates the secretion of a hormone in another endocrine gland

• TSH (thyroid stimulating hormone) stimulates the thyroid gland to produce thyroid hormone
• ACTH (adrenocorticotropic hormone) stimulates the adrenal cortex to produce cortisol
• FSH (follicle stimulating hormone) and LH (leutinising hormone) stimulate the gonads to produce gametes as well as sex hormones

Question 13

what is the relationship between the hypothalamus and pituitary gland?

Answer 13

they work together the control other endocrine glands.

Question 14

explain how the regulating hormones secreted from the hypothalamus exert their effects on the anterior pituitary.

Answer 14

releasing and inhibiting hormones secreted by neurons in the hypothalamus travel via the blood to the anterior pituitary to stimulate or inhibit release of the appropriate anterior pituitary hormone

Question 15

what is the most plentiful anterior pituitary hormone?

Answer 15

human growth hormone

• released in bursts every few hour by somatrophs
• their activity is controlled by two hypothalamic hormones: growth hormone-releasing hormone (GHRH) and growth hormone-inhibiting hormone (GHIH)

Question 16

explain the function of the posterior pituitary.

Answer 16

part of the brain ad is composed of neural tissue. it is connected to the hypothalamus via a nerve bundle

does not synthesise any hormones, but stores and releases from axon terminals two hormones produced by the neurosecretory cells of the hypothalamus; oxytocin and anti-diuretic hormone

Question 17

describe the antidiuretic hormone (ADH).

Answer 17

the amount of ADH secreted varies with blood osmotic pressure. function is to decrease urine output.

Question 18

where is the thyroid gland situated?

Answer 18

two lobes of the thyroid are located in the soft tissue of the neck on either side of the trachea. they are connected by an isthmus just below the thyroid cartilage

Question 19

which hormones are produced by the thyroid gland and what are their functions?

Answer 19

• T3 (tri-iodi-thyronine) a very potent hormone which increases the BMR and stimulates cells to increase their glucose utilisation
• T4 (tetraiodothyronine) less potent, is converted into T3. regulates growth and development, especially of nervous tissue and reproductive system

Question 20

what are the roles of T3 and T4?

Answer 20

• increase basal metabolic rate
• help maintain normal body temperature
• stimulate protein synthesis
• increase the use of glucose and fatty acids for ATP production

Question 21

what regulates release of thyroid hormones?

Answer 21

thyrotropin-releasing hormone (TRH) from the hypothalamus and thyroid-stimulating hormone (TSH) from the anterior pituitary stimulate synthesis and release of thyroid hormones

Question 22

what type of gland is the pancreas and where is it situated?

Answer 22

both an endocrine and exocrine gland, locates in the curve of duodenum

Question 23

name the two major hormones that are produced by the pancreas and describe their function.

Answer 23

insulin, produced by beta cells

• essential for the entry of glucose in most body cells
• inhibits breakdown of glycogen into glucose
• inhibits the conversion of amino acids or fats into glucose

glucagon, produced by alpha cells
increases blood glucose levels in three ways:
- breakdown of glycogen into glucose
- synthesis of glucose from lactic acid and non-carb molecules
- release of glucose from the liver

Question 24

what are the three main stress hormones?

Answer 24

adrenaline, noradrenaline, cortisol

Question 25

describe the effects of each of the stress hormones and state where these hormones are produced.

Answer 25

adrenaline and noradrenaline are both produced in the adrenal medulla

• triggers all of the fight or flight responses, increase HR and BP, cause pupillary dilation, bronchodilator and sweating
• noradrenaline released by post-ganglionic, sympathetic nerve terminals and adrenal medulla
• adrenaline is released b the adrenal medulla
• cortisol is produced in the adrenal cortex

Question 26

describe the structure of the kidney.

Answer 26

1. divided anatomically into the cortex surrounding a medulla and hilum
2. the cortex contains millions of blood filters
3. the renal medulla is divided into renal (medullary) pyramids, with renal columns, made of cortisol tissue, between them
4. the renal medulla is hypertonic to the filtrate in the nephron and hence aids in the reabsorption of water

Question 27

what is the function of the kidneys?

Answer 27

• removal of wastes (e.g. urea and creatinine)
• regulation BP
• regulation of water, pH, electrolytes
• erythropoiesis
• vitamin D activity