Hypothalamus-Pituitary-Target Organ Axes: Feedback Control II Flashcards
What is considered primary and secondary when discussing hypo and hyper secretory conditions in Anterior Pituitary Hormones?
Primary is the hypo or hypersecretion of the anterior pituitary cells
Secondary is the hypo or hypersecretion of the hypophysiotropic hormones
What is meant by hypophysiotropic hormones?
The secretory or inhibitory hypothalamus hormones such as GHIH
What is Panhypopituitarism?
It is the decrease in secretion in all anterior pituitary hormones
Panhypopituitary Dwarfism is associated with which group of individuals?
Children
True or False: The body’s physical parts develop in proportion to one another
In general, yes true
Discuss Panhypopituitary Dwarfism (3 sentences)
- It is the deficiency of anterior pituitary hormones during childhood.
- Rate of development of the individual is greatly decreased
- Individual never passes through puberty as they never secrete sufficient quantities of gonadotropic hormones to develop adult sexual functions.
True or False: Panhypopituitarism in the adult and hypothyroidism are linked
True
Discuss Panhypopituitarism in the Adult (3 points)
- It is the decreased secretion in all anterior pituitary hormones leading to hypothyroidism.
- There is depressed production of glucocorticoids by adrenal glands => less cortisol
- There is suppressed secretion of gonadotropic hormones leading to loss of sexual function
How is Panhypopituitarism in the adult treated?
It is treated with adrenocortical and thyroid hormones
True or False: The growth hormone is wholly responsible for determining the rate and final magnitude of growth
False: It is essential for growth but other hormones and genes are resposible for determining rate and final magnitude of growth
What are other growth-influencing hormones?
Thyroid hormone and sex hormones
Give 3 aspects that determine rate and final magnitude of growth
Genetic determination
Adequate diet
Freedom from chronic disease/stressful environment
Normal levels of growth-influencing hormones (such as thyroid hormone and sex hormones)
What is the most abundant hormone produced by the anterior pituitary?
Growth Hormone
At what ages do you expect the highest and lowest levels of growth hormone in the body? Give the approximate concentrations (just be close)
Highest levels from infancy to young adult (5-20) at 6 ng/ml
Lowest levels in late adulthood and elders (40-70) at 1.6 ng/ml
How is age related to GH secretion?
As age increases, secretion decreases
Once growth has ceased, are GH concentrations in the blood still significant?
Yes
Other than growth itself, what is another major effect of GH?
Metabolic Effects
What are the target organs that GH binds to in order to exert its metabolic effects?
Adipose tissue, skeletal muscles, and liver
What’re the effects of GH on adipose tissue?
Increases mobilization of fatty acids from adipose tissue => increasing fatty acids in the blood and increased use of fatty acids for energy.
What are the effects of GH on glucose in the body
GH decreases the rate of glucose utilization throughout the body => increasing blood glucose. This is done by decreasing muscle uptake of glucose which is important in conserving glucose for the brain.
What is the effect of GH on insulin
GH causes GH-induced insulin resistance
What are the effects of GH on the rate of protein synthesis?
Increases the rate of protein synthesis in most cells of the body
Metabolic disturbances due to excess GH secretion are very similar to what disease?
Type II diabetes
List the metabolic effects of GH on the body
- Increases mobilization of fatty acids from adipose tissue
- Decreases rate of glucose utilization throughout the body (decrease muscle intake and GH induced insulin resistance)
- Increases the rate of protein synthesis in most cells of the body
How does GH exert its growth-promoting effects?
GH does not act directly on its target cells. It enhances protein synthesis and bone growth.
GH exerts the majority of its growth-promoting effects indirectly by stimulating somatomedins
Give an example of somatomedins and give its structure and sources
Somatomedins are structurally and functionally similar to insuline. An example is IGF-1 or insulin-like growth factor 1.
The major source of circulating IGF-1 is the liver and is released into the blood on GH stimulation. It is also produced by most other tissues but only for local use and is not released into the blood.
Another name for IGF-1
Somatomedin C
Describe and Explain the effects of GH on bone growth
GH promotes growth of bone in length and thickness.
Length: Chondrocytes undergo cell division where older chondrocytes grow larger. Once older chondrocytes die, their matrix becomes calcified.
Thickness: Thickness increases by adding new bone on top of existing bone using osteoblasts. GH stimulates reproduction of these cells. Osteoclasts then remove older bone hence increasing thickness.
Explain the control of GH secretion
Hypothalamic Hypophysiotropic hormones such as GHRH and GHIH (Somatostatin). Increase and decrease secretion and synthesis.
Negative Feedback loops involving IGF-1 and GH. High blood levels of IGF-1 lead to decreased GH secretion by stimulating release of GHIH from the hypothalamus and hence suppressing somatotrophs in the anterior pituitary. GH inhibits GHRH and stimulates GHIH secretion.
Describe Diurnal rhythm as a factor influencing GH secretion
Diurnal rhythm is the Day/night rhythm of GH secretion. During most of the day, levels are fairly low and constant. Approximately 1 hour after onset of deep sleep, secretion increases (5x daytime values) and then rapidly drops over several hours
What are other factors (other than Diurnal Rhythm) influencing GH secretion
Think about the function of GH when remembering these
Exercise, stress, low blood glucose, increase in blood amino acids after a high protein meal, a decline in blood fatty acids.
Example: Remember that exercise, stress = low glucose in blood and GH conserves glucose levels in blood hence it is secreted
What are the causes of GH deficiencies and classify them as primary and secondary when applicable
- Hypothalamic dysfunction (secondary)
- Pituitary Defect (somatotrophs) (primary)
- Target Cells for GH fail to respond normally due to mutations in GH receptor
True or False: Symptoms of GH Deficiencies are dependent on genetic predisposition
False They are dependent on age
Hyposecretion of GH in children can lead to 3 conditions involving short stature. Name the 3 conditions.
Dwarfism
Laron Dwarfism
African Pygmies
State the diagnosis of Laron Dwarfism
Normal GH blood levels but abnormal GH receptors on tissues
State the diagnosis of African Pygmies
GH levels and target cell responsiveness normal but lack IGF-1
How does the lack of IGF-1 affect GH activity
Deficient growth function of GH but metabolic function remains normal
True or False: GH deficiency is more severe in adults than children
False, more severe in children
Describe symptoms of GH deficiency in adults
Reduced skeletal mass and strength
Decreased bone density
Increased risk of heart failure
Once insulin is released in the body, how does this affect GH levels. What is the response when GH deficiency is present?
Once insulin is released, this indicates that blood glucose levels were high and hence insulin drives glucose levels down. Low glucose levels stimulates GH secretion to conserve blood glucose => glucose levels increase. If there is deficiency then there is little to no response
What can cause excess GH secretion? Give a primary and secondary cause
Tumor of somatotrophs in the anterior pituitary. (Primary)
Defect in the mechanisms regulating GH secretion (Hypothalamic Hypophysiotropic hormones) (secondary)
True or False: Symptoms of excess GH secretion is also dependent on age
True
True or False: Overproduction of GH in children can lead to increased risk of diabetes
True
True or False: Increased production of GH in adults can increase risk of Hyperglycemia
True
Give 1 symptom of excess GH production in children
Gigantism: Rapid growth in heigh without distortion of body proportions. Also increases risk of Hyperglycemia => Increased risk of diabetes
Describe the effects/symptoms of excess GH secretion in adults
After adolescence, the person cannot grow taller but bones do become thicker causing Acromegaly.
Individuals may show increased thickening in extremities, face, hands, feet etc..
This can also lead to peripheral nerve disorders and insulin resistance => Hyperglycemia
What term is associated to individuals that show bone thickening in their extremities and face.
Acromegaly
A patient had their blood sampled before and after a glucose loading dose. What is expected to happen if it was a normal individual vs an individual with Acromegaly?
Normally, an increase in glucose should cause stimulation of GHIH to inhibit secretion of GH and hence there should be a decreased amount of GH.
If the patient with Acromegaly was sampled, then the decrease would not be significant hence confirming they have excess GH.
How is a patient with excess GH treated?
Somatostatin mimetics (such as GHIH)
Extended or excessive use of GH increases the likelihood of: Give 3 examples
Diabetes, kidney stones, high BP, joint pain, Carpal Tunnel Syndrome, Cancer
Where is prolactin produced?
Anterior pituitary cells, lactotrophs
State the role(s) of Prolactin
Stimulates breast development and milk production
Influences reproductive function and immune responses
Under what state does prolactin secretion increase?
Pregnancy
After delivery, when does prolactin levels fall?
3-6 weeks if no lactation and 8-12 weeks if suckling is maintained
Describe the regulation of Prolactin secretion
There are two hypothalamic hypophysiotropic hormones; PIH/dopamine, and PRH
PRL also inhibits its own secretion via short-loop feedback by increasing synthesis and release of PIH
State the Biological effects of Prolactin:
- Before and After Puberty
- During pregnancy
- Post-partum
- Stimulates proliferation and branching of ducts in female breast
- Causes development of lobules of alveoli within which milk is produced
- Stimulates milk synthesis and secretion
State the role of prolactin in reproduction
Prolactin blocks synthesis and release of gonadotropic-releasing hormone hence preventing ovulation in women and sperm production in men
Explain Prolactin’s role in immunity
Prolactin is synthesized by maternal uterine cells during pregnancy. This is important as it is required for acceptance of fetal tissue by mother and protection of maternal tissues from fetal invasion
Give the symptom of prolactin deficiency
Inability to lactate in women
Menses
Menstruation
Give the symptoms of excess prolactin in:
- Women
- Men
- Both Sexes
- Infertility and loss of menses
- Decreased testosterone and sperm production. Increased breast development and lactation (rare)
- Libido Decreased (sex drive)
What is the most common pituitary tumor and what does it lead to?
Lactotroph tumors, female infertility
Prolactin has a similar ancestral origin to what other hormone?
GH
What hormones are produced in the posterior pituitary? What type of hormones are they
Oxytocin and Vasopressin. They’re both peptide hormones
What Hypothalmic nucleus produces Oxytocin; Vasopressin
Vasopressin is produced by the supraoptic nucleus and oxytocin is produced in the paraventricular nucleus
State the functions of Oxytocin
- Causes milk ejection from lactating breast by contracting cells of the alveoli of the mammary gland
- Causes contraction of uterus during labor
What is the function of Oxytocin in men?
No function/unclear function
True or False: Milk ejection requires suckling of the infant to be ejected
True
What stimulates oxytocin secretion and what type of regulation is that?
Secretion of oxytocin is increased by reflexes when infant suckers and within the birth canal during childbirth. This is an example of positive feedback
What is another name for Vasopressin
ADH
State the 2 functions of Vasopressin
- Retention of water by kidneys
2. Contraction of arteriolar smooth muscle (vasoconstriction)
How is ADH secretion stimulated/inhibited?
- Water deprivation (Increased Osmolality of plasma and fluids bathing the brain). Water ingestion inhibits ADH
- Decreased blood volume or blood pressure stimulates ADH release.
What are the receptors or sensors that fire for ADH?
Osmoreceptor for Osmolality
Baroreceptor for blood pressure/volume
How and where is hypovolemia detected?
Hypovolemia is detected by pressure sensors of baroreceptors found in the walls of the left atrium and pulmonary veins known as the carotid and aortic baroreceptors.
What is the relationship between age and ADH secretion
Older individuals secrete more ADH than younger individuals
True or False: Pain, emotional stress, and Heat causes increased ADH secretion
True
True or False: Ethanol or Alcohol is an inhibitor of ADH secretion
True
Vasopressin deficiency leads to what disease most commonly?
Diabetes Insipidus
