Chapter 18: Endocrine System

What primary factor determines each cell's hormonal sensitivities?

A cell's hormonal sensitivities are determined by the presence or absence of the receptor complex needed to bind a given hormone.

Define hormone

A hormone is a chemical messenger that is secreted by one cell and travels though the bloodstream to affect the activities of cells in other parts of the body

How would the presence of a substance that inhibits the enzyme adenylate cyclase affect the activity of a hormone that produces its cellular effects by way of the secondary messenger cAMP?

A substance that inhibits adenylate cyclase, the enzyme that converts ATP to cAMP, would block the action of any hormone that requires cAMP as a second messenger.

What signs and symptoms would you expect to see in an individual whose diet lacks iodine?

An individual whose diet lacks iodine would be able to form the thyroid hormone T3 and T4. As a result, you would expect to see signs and symptoms associated with their deficiency: decreased metabolic rate, decreased body temperature, a poor response to physiological stress and an increase in the size of the thyroid gland (goiter).

What effect would elevated circulating levels of cortisol, a steroid hormone from the adrenal cortex, have on the pituitary secretion of ACTH?

Elevated circulating levels of cortisol inhibit the endocrine cells the control the release of ACTH from the pituitary gland, so ACTH levels would decrease. This is an example of negative feedback mechanism.

Roger has been extremely thirsty. He drinks numerous glasses of water everyday and urinates a great deal. Name two disorders that could produce these signs and symptoms. What test could a clinician perform to determine which disorder Roger has?

Extreme thirst and frequent urination are characteristics of both diabetes insidious and diabetes mellitus. To distinguish between the two, glucose levels in the blood and urine could be measured. A high glucose concentration would indicate diabetes mellitus.

If a person were dehydrated, how would the amount of ADH released by the posterior pituitary lobe change?

In dehydration, blood osmotic concentration is increased, which would stimulate the posterior lobe of the pituitary gland to release more ADH.

Julie is pregnant but is not receiving prenatal care. She has a poor diet consisting mostly of fast food. She drinks no milk, preferring colas instead. How would this situation affect Julie's level of parathyroid hormone?

Julie's poor diet would not supply enough Ca2+ for her developing fetus, which would remove large amounts of Ca2+ from the maternal blood. A lowering of the mother's blood Ca2+ would lead an increase in parathyroid hormone levels and increased release of stored Ca2+ from maternal bones.

When a person's thyroid gland is removed, signs of decreased thyroid hormone concentration do not appear until about one week later. Why?

Most of the body's reserves of the thyroid hormones T4, T3 are bound to blood-borne proteins called thyroid-binding globulins. Because these compounds represent such a large reservoir of T4 and T3, it takes several days after removal of the thyroid gland for the blood levels of T4 and T3 to decline.

How could you distinguish between a neural response and an endocrine response on the basis of response time and duration?

Neural responses occur within fractions of a second and are of short duration. Endocrine responses are slow to appear but last for minutes todays.

What are two benefits of having a portal system connect the median eminence of the hypothalamus with the anterior lob of the pituitary gland?

One benefit of the portal system is that it ensures that the controlling hormones will be delivered directly to the target cells. Secondly, because the hormones go directly to their target cells without first passing through the general circulation, they are not diluted. The hypothalamus can control the cells of the anterior lobe of the pituitary gland with much smaller amounts of releasing and inhibiting hormones than would be necessary if the hormones had to first go through the circulatory pathway before reaching the pituitary.

Describe paracrine communication

Paracrine communication is the use of chemical messengers to transfer information from cell to cell within a single tissue.

Sherry tells her physician that she has been restless and irritable lately. She has a hard time sleeping and complains of diarrhea and weight loss. During the examination, her physicians notices a higher-than-normal heart rate and a fine tremor in her outstretched fingers. What tests could the physician perform to make a positive diagnosis of Sherry's condition?

Sherry's signs and symptoms suggest hyperthyroidism. Blood tests could be performed to assay the levels of TSH, T3 and T4. From these tests, the physician could make a positive diagnosis (hormone levels would be elevated in hyperthyroidism) and also determine whether the condition is primary (a problem with the thyroid gland) or secondary (a problem with hypothalamo-pituitary control of the thyroid gland)

The release of which pituitary hormone would lead to an increased level of somatomedins in the blood?

Somatomedins mediate the action of growth hormone. Elevated levels of growth hormone typically accompany elevated levels of somatomedin.

Identify four mechanisms of intercellular communication

The four mechanisms of intercellular communication are direct, paracrine, endocrine and synaptic.

Pamela and her teammates are considering taking testosterone supplements (anabolic steroids) to enhance their competitive skills. What natural effects of this hormone are they hoping to gain? What additional side effects might these women expect should they begin an anabolic steroid regime?

The natural effects of testosterone are to increase muscle mass, increase endurance and enhance the "competitive spirit." Side effects in women include hirsutism (abnormal hair growth on the face or body), enlargement of the laryngeal cartilages, premature closure of the epiphyseal cartilages and liver dysfunction.

Identify the two lobes of the pituitary gland.

The two lobes of the pituitary gland are the anterior lobe and the posterior lobe.

Identify the hormones of the thyroid gland.

Thryoxine (T4), Triiodothyronine (T3) and calcitonin (CT)