Posterior Pituatory

Explain how structure and function relate within the posterior pituitary gland Recognize the role of anti-diuretic hormone (ADH) in body water regulation Explain the actions of oxytocin with respect to lactation Describe the actions of oxytocin during parturition Describe the important posterior pituitary disorders recognized in animals

What are the 2 hormones from the posterior pituatory gland and how are they connected

• ADH (urine)

• Oxytoin (mammary gland- Uterus)

Neurologically connected

What does ADH do..

• Distal tubule

• allows water reabsorption from the kidney

• more adh - more concentrated urine

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What foes diuresis refer too and what is diuretic

• Diuresis = increased urine output

• Diuretics increase that urine output

Gross Kidney anatomy

Nephron anatomy

signs of poor adh

§Excessive urination (polyuria)

§Excessive drinking (polydipsia)

What are osmoreceptors and where are they

• hypothalamus

• detects ECF osmolarity

• More conc = higher osmolarity

• More adh released = more water conserved therefore decreasing the blood concentration. IF the blood is too concentrated, then the hypothalamus will send a neurological signal to the posterior pituatory to release more ADH so that more water is reabsorped and the blood is diluted..

What other receptors can detect dehydration

• stretch receptors, e.g. baroreceptors

• respond to changes in hypotension, e.g. if the bp is too low, then more water will move in via osmosis, this will increase the overall blood pressure..

What is the overall hydration regulation..

§Osmoreceptors are the most sensitive

§Thirst stimulation is the major method of correcting dehydration

§Release of ADH helps to conserve water

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§Volume receptors in veins and atria only triggered by a large decrease in volume

§However, large amounts of ADH released when triggered (an emergency response!)

What does adh do to the distal tubule

• increases the number of aqua porins therefore more water is reabsorped

§ADH binds to receptors

§Activation of adenyl cyclase

§Production of cAMP

§Vesicles containing aquaporins move to cell surface

§Inserted via exocytosis

§Proportional to plasma ADH concentration

§Removed via endocytosis

What are the 2 tyopes of diabetes insipidus

§Neurogenic diabetes insipidus

§Inadequate ADH release from pituitary

§2. Nephrogenic diabetes insipidus

§Inadequate response within the kidney

Diagnosis of Diabetees insipidus?

HOw does oxytocin work

• smooth muscle cells during uterine contraction - neuronally regulated

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What are the stages of how oxytocin works at birth..

§Stages of parturition

  Stage 1: Myometrial contractions and dilation of the cervix

  Stage 2: Expulsion of the fetus through birth canal

  Stage 3: Expulsion of the placenta

§Fetus engages the cervix in Stage 2

§Neuroendocrine reflex

What is the neuroendocrine reflex during birth

• nerves are stimulated in the cervix

• afferent nerve impulses to hypothalamus

• neuroendocrine paraventricular + supraoptic nucleas hypothalamus

• oxytoxin secreted from the pars nervosa (posterior pituitary)

• enters blood circularion and acts on muscle for strong uterine contractions

Clinical relavance oxytocin

§Oxytocin can be administered to induce parturition many species (example – horse)

§Treatment for uterine inertia

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Retained Placenta

§Oxytocin will induce contractions and help to expel the placenta

§Used to clear fluid from the uterus (metritis)

How does oxytocin stimulate milk let -down

• binds to myopepithelial cells

• orientated along long axis of secretory duct whcih becomes shorter and wider

• sphyncter muscle of teat relax

How does oxytocin work in terms of neural transmission

• high density nerve fibres teats.. superficial sensory pathways + inguinal nerve

• afferent sensory neurones enter the lumbar segments of the spinal cord

• ascend nerve fibre and causes oxytocin to be released from the nerve endings,

Oxytoxin mammary response

§Slower than a nervous system response

§1 second for sensory arc (teat to hypothalamus)

§Another 1 second for oxytocin release (hypothalamus to pituitary gland)

§20 seconds for blood to reach mammary gland

§Few seconds to push milk out of alveoli, 20 to 30 seconds for cisternae to fill

What affect foes oxytoxin have on mammary galnds..

• increases alveoli pressur e

• 0 reduces resistance in excretory ductrs and teat canal

• causes increased milk outlflow

• oxytocin will induce milk let down + for weak calves

how does oxytocin cause milk let down

triggers the alveoli, containing the milk to contract adn forc e it out.