Chapter 76

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What is the pituitary gland divided into?

Anterior and posterior pituitary

Which are the hormones of anterior pituitary?

Growth hormone (affects protein formation, cell differentiation), adrenocrticotropin (corticotropin), t hyroid-stimulating hormone (thyrotropin), prolactin, follicle stimulating hormone and luteinizin hormone, antidiuretic hormone, oxytocin

What does thyroid-stimulating hormone do?

It controls the secretion rate of thyroxine and triiodothyronine by thyroid gland

What does prolactin do?

It promotes mammary gland development and milk production

What do follicle-stimulating hormone and luteinizing hormones do?

They control growth of ovaries and testes

What does oxytocin do?

It helps express milk from glands of breast to nipples during suckling and helps in delivery of baby at end of gestation

Which are the cell types of anterior pituitary gland?

1. Somatotropes (human growth hormone hGH)
2. Corticotropes (adrenocorticotropin ACTH)
3. Thyrotropes (thyroid stimulating hormone TSH)
4. Gonadotropes (including luteinizig hormone and folliclestimulataing hormone)
5. Lactotropes (prolactin PRL)

What is the quantity of the different cell types?

About 30 to 40% of anterior pituitary cells are somatotropes that secrete growth hormone and baout 20% are corticotropes that secrete ACTH, each of the other cell types accounts for only 3% of the total

How do somatotropes stain?

They stain strongly witht acid dyes and are therefore called acidophils (pituitary hormones that secrete large quantities of human growth hormone are called acidophilic tumors)

Where are magnocellular neurons located?

In supraoptic and paraventricular nuclei of hypothalamus

Posterior pituitary hormones are secreted by bodies of cells (large neurons called magnocellular neruons), what happens next?

Hormones are transproted in axoplasm of neurons' nerve fibers passing from hypothalamus to posterior pituitary gland

What are secretion from posterior pituitary controlled by?

By nerve signals that originate in hypothalamus and terminate in posterior pituitary

What are secretion by anterior pituitary controlled by?

By hormones called hypothalamic releasing and hypothawlamic inhibitory hormones (or factors) secreted within hypothalamus and then conducted to anterior pituitary through blood vessels called hypothalamic-hypophysial portal vessels

What do oflactory stimuli do?

They denote pelasant or unpleasant smells transmit strong signals directly and through amygdaloid nuclei into hypothalamus

What can inhibit various portions of hypothalamus?

Concentrations of nutrients, electrolytes, water and various hormones in blood

What is anterior pituitary gland?

It is a highly vascular gland with extensive capillary sinuses among glandular cells (blood enters sinuses passes through capillary bed in lower hypothalamus) the blood then flows through hypothalamic-hypophysial portal blood vessels into anterior pituitary sinuses

What is the median eminence?

It is the lowermost portion of hypothalamus, connecting inferiorly with pituitary stalk

What about the median eminence?

Small arteries penetrate into median eminence and then additional small vessels return t o its surface, coalescing to form the hypothalamic-hypophysial portal blood vessels

What do synthesize and secrete the hypothalamic releasing and inhibitory hormones that control secretion of anterior pituitary horones?

Special neurons in hypothalamus

Which are the major hypothalamic releasing and inhibitory hormones?1

Thyrotropin-releasing hormone (TRH) which casues release of thyroid-stimulating hormone

Which are the major hypothalamic releasing and inhibitory hormones?2

Corticotropin-releasing hormone (CRH), which casues release of adrenocorticotropin

Which are the major hypothalamic releasing and inhibitory hormones?3

Growth hormone-releasing hormone (GHRH) which casues release of growth hormone and growth hormone inhibitory hormone (GHIH) also called somatostatin, which inhibits release of growth hormone

Which are the major hypothalamic releasing and inhibitory hormones?4

Gonadotropin-releasing hormone which casues release of LH and FSH

Which are the major hypothalamic releasing and inhibitory hormones?5

Prolactin inhibitory hormone (PIH) which causes inhibition of prolactin secretion

Which of the anterior pituitary hormones exert principal effects stimulating target glands including thyroid gland, adrenal cortex?

All major anterior pituitary hormones, except for growth hormone

What is growth hormone also called?

Somatotropic hormone or somatotropin

What does growth hormone lead t o?

Increased mitosis

What other effects does growth hormone have?

1) increased rate of protein synthesis 2) increased mobilization of fatty acids from adipose tissue, increased free fatty acids in blood an increased use of fatty acids for energy 3) ddecreased rate of glucose utilization throughout body

What does growth hormone also lead to regarding proteins?

Protein deposition

What does growth hormones do with amino acids?

Enhance transport of most amino acids through cell membranes to the interior of cells

What does growth hormone do with RNA translation?

it increases RNA translation, causing protein to be synthesized in greater amounts by ribosomes in cytoplasm

What does growth hormone do with transcription of DNA?

It stimulates transcription of DNA in nucleus, causing fomration of increased quantities of RNA promotoing protein synthesis

How can we summarize the purpose of growth hormone?

It enhances almost all facets of amino acid uptake and protein shynthesis by cells, while at the same time reducing breakdown of proteins

What does growth hormone do with fatty acids?

It converses fatty acids to acetyl-CoA

What happens under influence of excessive amounts of growth hormone?

Fat mobilization from adipose tissue becomes so great that large quantities of acetoacetic acid are formed by liver and relesaed into body fluids causing ketosis

What multiple effects does growth hormone have?

1) decreased glucose uptke in tissues such as skeletal muscle and fat 2) increased glucose production by liver and 3 ) incerased insulin secretion

When does growth hormone fail to cause growth in animals?

In animals that lack a pancreas

What else does growth hormone stimulate?

Cartilage and bone growth by 1) increased deposition of protein by chondrocytic and osteogenic cells that cause bone growth 2) increased rate of reproduction of these cells

What is the first (out of two) principal mechanisms of bone growth?

In response to growth hormone stimulation, the long bones grow in length aat epiphyseal cartilages

What are somatomedins?

Growth hormone causes liver and other tissues to form several small proteins called somatomedins

What effect do somatomedins have?

Of increasing all aspects of bone growth

What are somatomedins also called?

Insulin-like growth factors (IGFs)

How many somatomedins are there and which is most important?

Four, and somatomedin C is most important

How does growth hormone attach to plasma proteins in blood?

Only weakly, therefore it is released from blood into tissues rapidly, having a half-time in blood of less than 20 minutes

How do somatomedin C attach itself?

It attaches strongly to a carrier protein in blood that like somatomedin C is produced in response to growth hormone, as a result somatomedin C is released only slowly from blood to tissues, with half-time of about 20 hours

What are stimulated to secrete growth hormone?

1) starvation 2) hypoglycemia (low concentration of fattty acids in blood) 3) exercise 4) excietement 5) trauma and 6) ghrelin, during first 2 hours of deep sleep

What is the normal concentration of growth hormone in plasma of adult?

Between 1,6 and 3 ng/ml and in a child or adolescent 6 ng/ml

Kwashiorkor?

High levels of growth hormone with protein deficiency (carbohydrates can not be used as a treatment) protein supplements leads however to a decrease in the growth hormone (kwashiorkor symptom treated)

Which is the part of hypothalamus that causes secretion of GHRH?

Ventromedial nucleus

What increase the rate of growth hormone secretion?

Catecholamines, dopamine and serotonin

What does Panhypopituitarism mean?

Decreased secretion of all anterior pituitary hormones (which can be from birth or occur suddenly) due to pituitary tumor destroying pituitary gland

Which are the general effects of adult panhypopituitarism?

1) hypothyroidism 2) depressed production of glucocorticoids by adrenal glands 3) suppressed secretion of gonadotropic hormones so that sexual functions are lost

Dwarfism?

Does not pass through puberty and never secretes sufficient quantities of gonadotropic hormones to develop adult sexual functions. (African pygmy and Levi-Lorain dwarf means that rate of growth homrone secretion is normal or high but inability to form somatomedin C)

Growth hormone of the human being is called what?

Human growth hormone, to distinugish it from the others

How can human grwoth hormone now be syntehsized?

By Escherichia coli bacteria as a result of successful application of recombinant DNA technology

Gigantism?

Acidophilic growth hormone-producing cells of anterior pituitary gland become active so that acidophilic tumors occur in the gland

What does gigantism lead to?

Large quantities of growth hormone are produced, all body gtissues grow rapildly

What does the giant have?

Hyperglycemia, diabetes mellitus can also develop

What is gigantism causing if left untreated?

Pituitary gland will grow until the gland is destroyed, which can lead to general deficiency of pituitary hormones causing death in early adulthood

Acromegaly?

Acidophilic tumor, person cannot grow taller, but bones can become thicekr and soft tissues can continue to grow

Where is enlargement mostly in acromegaly?

In bones of heands and feet and in membranous bones, including cranium, nose, bosses on the forehead, supraorbital ridges and more

What is a consequence of Acromegaly?

Lower jaw protrudes foward, forehead slants forward, nose increases in size, feet require larger shoes and fingers become thickened, and kyphosis occurs

People who have lost ability to secrete growth hormone what happens?

Some features of aging process accelerate, 50-year old person without growth homrone may have apearance of a person aged 65 years old

Why do people look older due to lack of growth hormone?

Because of decreased protein deposition in tissues of body and increased fat deposition in its place

What are posterior pituitary glands composed of?

Pituicytes (cells)

What do pituicytes do?

They do not secrete hormones, but act as asupportin strucuter for terminal nerve fibers and temrinal nerve endigns from nerve tracts that originate in supraoptic and paraventricular nuclei of hypothalamus

What do the nerve endings secrete?

Two posterior pituitary hormones 1) antidiuretic hormone (ADH, vasopressin) and oxytocin

Where is ADH formed primarily?

In supraoptic nuclei

Where is oxytocin formed primarily?

In paraventriuclar nuclei

How are the hormones released from the secretory granules in nerve endings by what method?

By exocytosis and is absorbedi nto adjacent capillaries

What are the differences between vasopressin and oxytocin?

These two hormones are almost identical except that in vasopressin, phenylalanine and arginine replace isoleucine and leucine of oxytocin molecule

What does oxytocin do?

It stimulates contraction of pregnant uterus, especially toward end of gestation

What happens during labor?

Amount of oxytocin in plasma increases 3) and stimulation of cervix in a pregnant animal elicits nervous signals that pass to hypothalamus and causei ncreased secretion of oxytocin

What role does oxytocin also have?

In lactation, when oxytocin causes milk to be expressed from alveoli into duts of breast so that baby can obtain it by suckling

How is milk ejection by breasts done?

Suckling (sugning) causes signals to oxytocin neurons in paraventricular and supraoptic nuclei in hyptohalamus causing release of oxytocin, causing contraction of myoepithelial cells, milk begins to flow

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