Pituitary Gland - Posterior pituitary

Question 1

Posterior pituitary

• aka
• function
• blood supply
• main consequence of disease

Answer 1

• neurohypophysis
• nervous tissue: storehouse for hormones made in hypothalamus (ADH and oxytocin)
• inferior hypophyseal arteries
• disordered water homeostasis

Question 2

Posterior pituitary

- innervation

Answer 2

Directly innervated by hypothalamic neurons

• Supraoptic nucleus: ADH
• Paraventricular nucleus: oxytocin

Question 3

Posterior pituitary

- what might cause neuronal damage?

Answer 3

lesions that affect pituitary stalk or hypothalamus

Question 4

Oxytocin

Answer 4

stimulates postpartum milk letdown in response to suckling

Question 5

ADH

• released when
• action

Answer 5

• low bp/volume, high plasma osmolality, pain, emotional stress
• action: concentrates urine by increasing water reabsorption in the kidney

Question 6

Describe osmoreceptors that are related to ADH

Answer 6

• located in supraoptic nucleus

- aid in ADH release and thirst regulation

Question 7

What inhibits ADH

Answer 7

• high bp
• low plasma osmolality
• alcohol

Question 8

Diabetes insipidus

- etiology

Answer 8

• no association with DM
• damaged pituitary gland or hypothalamus
• disrupts nl production, storage, release of ADH
• pass abnl large volume urine that is “insipid”

Question 9

Diabetes insipidus

- ADH changes

Answer 9

• loss of ADH secretion OR action
• decreased ADH = less water reabsorption
• increased dilute urine output
• increased serum concentration
• Euvolemic hypernatremia

Question 10

4 types of Diabetes insipidus

Answer 10

• central
• nephrogenic
• disogenic
• gestational

Question 11

Diabetes insipidus

- central

Answer 11

• primary: genetic abnormality of ADH gene or idiopathic

- secondary (MC): Sx, skull base fx/cranial injury, suprasellar/intrasellar tumor, infection

Question 12

Diabetes insipidus

- nephrogenic

Answer 12

kidneys do not have normal response to ADH, usually dt tubule defect (inherited or CKD)

Question 13

Diabetes insipidus

- disogenic

Answer 13

problem with thirst mechanism, often associated with mental illness

Question 14

Diabetes insipidus

- gestational

Answer 14

• placenta breaks ADH down and produces prostaglandins, reducing kidney’s sensitivity to ADH

Question 15

Diabetes insipidus

- signs and sx

Answer 15

• abnl large volume dilute urine
• polyuria, enuresis, nocturia
• thirst, polydipsia
• dry skin, dizzy, nausea, confusion
• low bp, hypernatremia

Question 16

Diabetes insipidus

- dx

Answer 16

• History and PE
• verify polyuria with 24h urine output collection (>50 ml/kg/day)
• check osmolarity
• check sodium
• water deprivation test
• MRI: not diagnostic but can help visualize tumor

Question 17

Osmolarity in Diabetes

Answer 17

> 300 due to solute diuresis, pt should be eval for DM or other causes of excessive solute excretion
< 300: due to water diuresis, should be evaluated for type of DI

Question 18

Diabetes insipidus

- how to distinguish between central and nephrogenic

Answer 18

• administer desmopressin (synthetic ADH)
• measure urine osmolality at timed intervals, an increase of >50% indicates central DI
• smaller/absent response suggests nephrogenic

Question 19

Diabetes insipidus

- tx of central

Answer 19

• mild: increase fluid

- otherwise: desmopressin (DDAVP)

Question 20

Diabetes insipidus

- tx of nephrogenic

Answer 20

• NO desmopressin
• low salt diet to reduce urine production
• increase fluids
• HCTZ

Question 21

Diabetes insipidus

- tx of gestational

Answer 21

• DDAVP

- deliver baby

Question 22

Diabetes insipidus

- tx of disogenic

Answer 22

• no tx…

- decrease fluid intake

Question 23

SIADH

- describe

Answer 23

• MC cause euvolemic hyponatremia in hospitalized pts

Question 24

SIADH

- define

Answer 24

hyponatremia and hyposmolality resulting from inappropriate and continued secretion/action of ADH despite normal/increased plasma volume
(retain too much water)

Question 25

SIADH | - urine

Answer 25

concentrated, impaired water secretion

Question 26

SIADH | - pathophysiology

Answer 26

- excessive ADH production = decreased volume of highly concentrated urine - water retention - elevated urine osmolality - decreased serum osmolality - hyponatremia dt excess water, not deficient sodium

Question 27

SIADH | - etiology

Answer 27

``` CNS - lesions, inflammatory dz - trauma, psychosis Drugs - nicotine, phenothiazines, TCAs, SSRIs and others Pulmonary - infection - mechanical/ventilatory issue ```

Question 28

SIADH | - signs and sx

Answer 28

``` Acute: - water intoxication - HA, confusion - Ataxia - Nausea, vomiting - anorexia - Coma, convulsions Chronic - may be asymptomatic ```

Question 29

SIADH | - Dx

Answer 29

- PMH: trauma, drug use, etc. - PE: euvolemic, normotensive - hyponatremia and hypoosmolality - renal excretion of na - concentrated urine - no volume depletion - no other causes of hyponatremia - fluid restriction corrects hyponatremia

Question 30

SIADH | - Tx goal

Answer 30

- correct hyponatremia at a rate that does not cause neurologic complications - increase serum na 0.5-1.0 mEq/h - no more than 10-12 mE in first 24 hours - rule of sixes (6 in 6 hours for severe sx and then stop)

Question 31

SIADH | - Acute tx

Answer 31

- fluid restriction - hypertonic saline (3%) - vasopressin receptor antagonists - furosemide (diuretic)

Question 32

SIADH | - chronic tx

Answer 32

- fluid restriction - vasopressin receptor antagonists - loop diuretics