Pituitary Gland and Its Disorders Flashcards
The pituitary gland has a dual blood supply.
What are these supplies?
- first is via long and short pituitary arteries
- second is from hypophyseal portal circulation (begins as a capillary plexus around Arc)
What 6 hormones are released from the anterior pituitary, and what is their role?
- Adrenocorticotrophic hormone (ACTH): regulation of adrenal cortex
- Thyroid-stimulating hormone (TSH): thyroid hormone regulation
- Growth hormone (GH): growth
- Luteinising hormone (LH) and Follicle-stimulating hormone (FSH): reproductive control
- Prolactin (PRL): breast milk production
What 2 hormones are released from the posterior pituitary, and what is their role?
- Anti-diuretic hormone (ADH) - osmoregulation
- Oxytocin: breast milk formation and uterine contractions
What are some different types of pituitary tumours?
HORMONE HYPERSECRETION
SPACE-OCCUPYING LESION:
- headaches
- visual loss (field defect)
- cavernous sinus invasion
HORMONE DEFICIENCY STATES:
- interfere with the surrounding normal pituitary
Tumours of the anterior pituitary can cause syndromes of hormone excess.
List the syndrome associated with the overexpression of each hormone from the anterior pituitary.
GH: Acromegaly
ACTH: Cushing’s Disease
TSH: Secondary thyrotoxicosis
LH/FSH: (non-functioning pituitary tumour)
PRL: Prolactinoma
Describe the control of growth hormone. PART 1
- Stimulatory hormone (GHSH) and inhibitory hormone (somatostatin).
- GH is released in pulses
- GH acts on the liver to produce certain growth factors e.g IGF-1, which causes long bone growth for linear growth.
Describe the control of growth hormone. PART 2
- Negative feedback is mainly supplied by the IGF-1.
- When there is pituitary tumour producing too much GH, affects our growth and metabolism.
What are some systemic effects of GH/ IGF-1 excess? PART 1
- Increased skin thickness
- Increased sweating
- Impaired glucose tolerance
- Diabetes mellitus
What are some systemic effects of GH/ IGF-1 excess? PART 2
- Insulin resistance
- Reduced total cholesterol
- Increased triglycerides
- Increased nitrogen retention
What are some consequences of GH/IGF-1 excess?
- Cardiomyopathy (diseases of the heart muscle)
- Hypertension
- Bowel polyps (small growths)
- Arthropathy (disease of a joint)
- OSA (obstructive sleep apnoea)
List some actions of cortisol on energy metabolism.
- increased gluconeogenesis/glycogenolysis
- decreased glucose utilisation
- increased glycogen storage
- increases lipolysis
- protein catabolism
List some other effects of cortisol.
- maintains BP
- anti-inflammatory effects.
- increased gastric acid production.
What happens as a result of Cushing’s Syndrome due to changes in fat metabolism?
- change in body shape
- central obesity
- thin skin, easy bruising
- osteoporosis (brittle bones)
- diabetes
What happens as a result of Cushing’s Syndrome due to changes in sex hormones and salt and water retention?
- excess hair growth
- irregular periods
- impotence
- high blood pressure
- fluid retention
List some drugs that interfere with dopamine and prolactin secretion.
- antiemetics (effective against vomiting and nausea)
- antipsychotics
- oral contraceptives/ hormone replacement therapy
What are some features of prolactin excess (hypogonadism)?
- infertility
- oligoamenorrhoea (irregular menstrual periods)
- amenorrhoea (no menstrual periods)
- galactorrhoea (milky discharge from breasts)
What is the treatment for prolactinomas?
Dopamine agonists (such as bromocriptine and cabergoline), not surgery.
Describe non-functioning pituitary tumours.
- No syndrome or hormone excess is produced
- Can cause symptoms due to space occupation (headaches, visual field defects)
- Treatment would be surgery - no effective medical therapy
What are possible treatments for pituitary adenomas? PART 1
SURGERY:
- transsphenoidal (through nose and sphenoid bone)
- adrenalectomy
RADIOTHERAPY (slow)
What are possible treatments for pituitary adenomas? PART 2
DRUGS:
- block hormone production and stop hormone release
List some causes of pituitary failure.
- tumour
- trauma
- infection
- inflammation (sarcoidosis [the abnormal collection of inflammatory cells], histiocytosis [excessive number of tissue macrophages])
- iatrogenic (illness caused by medical examination/ treatment)
What are the effects of hypopituitarism? PART 1
It affects the thyroid:
- bradycardia
- weight gain
- cold intolerance
- hypothermia
What are the effects of hypopituitarism? PART 2
It affects sex steroids:
- oligomenorrhoea
- reduced libido
- reduced body hair
What are the effects of hypopituitarism? PART 3
Reduces cortisol:
- tiredness
- weakness
- postural hypotension
- myalgia (pain in a muscle)
Reduces GH:
- tired
- central weight gain
What would be the treatment for hypopituitarism?
- For the thyroid effects, we would give thyroxine.
- For the sex steroid effects, we would give testosterone and oestrogen.
- For the reduced cortisol, we would give hydrocortisone.
- For the reduced GH, we would give GH.
What does vasopressin control?
CONTROL:
- increased plasma osmolality
- decreased BP (baroreceptors)
- decreased PaO2, increased PaCO2 (cortisol, sex steroids, angiotensin II)
Where does vasopressin act on?
- Collecting ducts, to increase permeability for H2O for the reabsorption of free water
- Vasoconstriction of blood vessel
Describe SIADH
- Too much ADH.
- Caused by a brain injury/ tumour, lung cancer or infection or metabolic cause such as hypothyroidism or Addison’s.
How can SIADH be diagnosed and treated?
Checking bodily fluids for:
- low plasma Na+
- low plasma osmolality
- high urine osmolality
- high urine sodium
Treatment would involve fluid restrictrion.
Describe Diabetes Insipidus
Underproduction of ADH in the body. The patients urinate until they dehydrate themselves.
- 2 main causes:
- CRANIAL - lack of ADH production
- NEPHROGENIC - receptor resistance
How would Diabetes Insipidus be diagnosed?
Checking body fluids:
- polyuria [excessive urinating] (more than 3L)
- polydipsia [excessive thirst] (increased Na+, increased plasma osmolality, decreased urine osmolality, decreased urine Na+)
What are the 2 functions of the hypothalamus?
→ it takes sensory input - electrical signal
→ and produces hormones to adapt to the physical state - chemical signal
What is the negative feedback system in endocrinology?
→ The production of the end hormone stops the pituitary and hypothalamus producing more
How is prolactin controlled?
→ The stimulus to production of milk is an external signal
→ Intrinsic high production of prolactin from the pituitary
→ Tonic inhibitory dopamine signal from the hypothalamus to the pituitary
How does lactation occur?
→ mechanical stimulation of the nipple sends a neuronal signal to the brain
→ goes to the hypothalamus
→ switches off dopamine production
What is homologous vision?
→ Nasal fibres from the same side cross and line up with temporal fibres on the other side
→ Go into one piece back to the brain for interpretation
Where is the optic chiasm?
Above pituitary
What is bitemporal hemianopia?
→ Partial blindness
→ Vision is missing in the outer half of both right and left visual field
What rises when a tumor is made?
→ prolactin
→ obstructs the pituitary and stops dopamine coming in the brain
