Pituitary Function and Failure Flashcards
What is the posterior pituitary?
Neurohypophysis
Outgrowth of brain - nervous tissue
Neural link to hypothalamus
What is the anterior pituitary?
Adenohypophysis
From glandular epithelial tissue, ectodermal cells
Vascular link to hypothalamus
In what ways are the anterior and posterior pituitary different?
Embryologically
Structurally
Functionally
What is the infundibulum?
Stalk connecting pituitary to brain
What does the posterior pituitary release?
Vasopressin/ADH
Oxytocin
What does ADH do?
Increases collecting duct permeability
Decreases urine volume
What does oxytocin do?
Breasts - contracts myoepithelial cells along ducts to eject milk
Uterus - contraction
Which hormone makes milk?
Prolactin
From what are the hormones of the posterior pituitary released into the general circulation?
Endings of supraoptic and paraventricular neurons
From what are trophins of the hypothalamus secreted?
Endings of arcuate and other hypothalamic neurons
To where are trophins of the hypothalamus secreted?
Portal hypophysial circulation
Where are the arcuate, supraoptic, and paraventricular nuclei?
Hypothalamus
What is the synthesis, storage, and release of posterior pituitary hormones?
- Hormone made and packaged in cell body of neuron in hypothalamus
- Vesicles transported down cell
- Vesicles containing hormone stored in posterior pituitary
- Hormones released into blood
Describe the steps involved in the activation of the anterior pituitary via the hypothalamic-hypophyseal portal system
- Neurons synthesising trophic hormones release them into capillaries of portal system
- Portal vessels carry trophic hormones directly to anterior pituitary
- Endocrine cells release hormones into second set of capillaries for distribution to rest of body
What is the hypothalamic-hypophyseal portal system?
Vascular system connecting hypothalamus to anterior pituitary
Why don’t you need much trophic hormone to be released from the hypothalamus?
Because hormone concentrated and rapid
What kinds of effects do the hormones released from the hypothalamus have on the anterior pituitary?
Sometimes releasing hormone
Sometimes inhibiting hormone
Both control anterior pituitary function
Is the action of dopamine on the breast direct or indirect?
Direct
What is the target pituitary cell of corticotropin-releasing hormone (CRH)?
Corticotroph
What are the hormone products of corticotrophs?
Adrenocorticotropic hormone (ACTH) Beta-lipotropin
What is the target tissue of ACTH?
Adrenal cortex > cortisol
What is the target tissue of beta-lipotropin?
Adipose tissue
What is the target pituitary cell of thyrotropin-releasing hormone (TRH)?
Thyrotroph
What are the hormone products of thyrotrophs?
Thyrotropin/thyroid stimulating hormone (TSH)
Prolactin
What is the target tissue of TSH?
Thyroid gland > thyroid hormones
What is the target pituitary cell of gonadotropin-releasing hormone (GnRH)?
Gonadotroph
What are the hormone products of gonadotrophs?
Luteinising hormone (LH) Follicle stimulating hormone (FSH)
What is the target tissue of LH and FSH?
Gonads > sex steroids
What is the target pituitary cell of growth hormone-releasing hormone (GHRH)?
Somatotroph
What is the hormone product of somatotrophs?
Somatotropin/growth hormone (GH)?
What is the target tissue of GH?
All tissues
What is the target pituitary cell of somatostatin/growth hormone-inhibiting hormone?
Somatotroph
What is the target pituitary cell of prolactin-releasing factor (PRF)?
Mammotroph
What is the hormone product of mammotrophs?
Prolactin
What is the target tissue of prolactin?
Breasts
Gonads
Does the hypothalamus-pituitary-adrenal cortex axis have short-loop negative feeedback?
No
What impacts on the function of the hypothalamus and pituitary?
Many structures
What is Kallmann syndrome?
Embryologically GnRH neurons failed to migrate via olfactory pathway
Hypogonadotropic hypogonadism
Hyposmia or anosmia = loss of smell
What is growth?
Net synthesis of proteins
Lengthening of long bones
Increased size and number of cells in soft tissues
What is needed for growth?
GH = essential
Other important factors
- Genetic determination
- Adequate diet
- No chronic disease/stressful environment
- Normal mix of growth-influencing hormones
What are some of the hormones influencing growth, other than GH?
Thyroid hormones
Insulin
Sex hormones
What determines size at birth?
Genetics
Environment; eg: drug exposure
Nutrition of mother
What has small birth weight been linked with in adulthood?
Risk of disease
When is the post-natal growth spurt?
First two years
What happens during the post-natal growth spurt?
70% brain growth
What is the growth from two years to adolescence?
Little sex difference in height and weight
Rate of linear growth declines
Can catch-up growth happen if you are born small?
Yes, if provided with adequate post-natal environment
When does the pubertal growth spurt happen?
Adolescence
What happens during the pubertal growth spurt?
Lengthening of long bones
Genetic and hormonal factors
Testosterone and oestrogen
Full adult height at end of adolescence
What are the metabolic effects of GH?
Increased blood fatty acid and glucose
During prolonged fasting/body’s energy needs exceeded
What are the effects of GH on soft tissue and the skeleton?
Hyperplasia and hypertrophy of soft tissues and skeleton
Increased protein synthesis
What is the effect of GH on insulin-like growth factors (IGFs)?
Increased IGFs from liver
What type of chemical is GH?
Peptide
How is GH transported in the circulation?
Half dissolved in plasma, half bound to binding protein
What is the half-life of GH?
18 min
What affects the release of GH?
Circadian rhythm of tonic secretion Influenced by - Circulating nutrients - Stress - Other hormones
What are the target tissues of GH?
Trophic on liver for IGFs
Acts directly on many cells
What controls GH?
GHRH
Somatostatin
What is the target receptor of GH?
Membrane receptor with tyrosine kinase activity
What are somatomedins?
IGFs: IGF-I and IGF-II = polypeptide growth factor
What are the effects of IGF?
Insulin-like activity
Antilipolytic activity
Protein synthesis
Epiphysial growth
What is required for protein and cell division in tissues?
GH
IGFs
What is the role of thyroid hormone in IGF activity?
Permissive
What is the role of insulin in tissue growth?
Supports growth
What is the role of oestrogen in bone growth?
Closes epiphyseal plates of long bones - in males and females
What nutrient is required for bone growth?
Ca
What is the relative importance of thyroid hormones in growth and development?
Important very early on in foetal and post-natal development
What is the relative importance of GH in growth and development?
Important in
- Brain development
- Juvenile and childhood life
What causes dwarfism?
Low levels of GH as child
What is Laron dwarfism?
GH insensitivity
GH receptors unresponsive
Normal GH
What is the effect of GH deficiency in adult onset?
Few effects
How is GH deficiency treated?
Genetically engineered human GH administered
What is cretinism?
Childhood hypothyroidism > no permissive activity
What is achodroplasia?
Most common form of dwarfism in humans
Fibroblast growth factor receptor 3 mutation
What are some GH independent causes of short stature?
Cretinism Precocious/early puberty Gonadal dysgenesis Constitutional delayed/stunted growth Psychosocial dwarfism Achondroplasia
What is gigantism?
Overproduction of GH as child before puberty
What is acromegaly?
Overproduction of GH as adult
Bone and soft tissue deformities
Increased viscera size and protein content