Hypothalamus and the Pituitary Gland Flashcards
How is the hypothalamus connected to the pituitary gland?
The hypothalamus is connected to the pituitary gland by the infundibulum.
What does hypothalamus literally mean?
The hypothalamus is a Greek word meaning ‘inferior to the thalamus’.
What does the hypothalamus structure allow?
It’s ultimate brain structure allows mammals to allow homeostasis of the body.
What is the hypothalamus anatomically?
It is a collection of neurons
What is the hypothalamus physiologically?
Physiologically, it is a master control centre that orchestrates coordinated response from the brain endocrine system and the autonomic nervous system.
What are the two parts of the pituitary gland?
The pituitary gland has two parts - posterior and anterior.
What inputs does the hypothalamus receives?
Sensory Input: temperature, pain, smell,light
cerebral cortex
Brain stem
Limbic system
Non-neuronal input: osmolality, blood viscosity, blood pressure, endocrine feedback
What does the hypothalamus do with received inputs?
All this inputs is taken into hypothalamus and coordinates outputs:
Temperature, sleep, thirst, appetite
Cerebral cortex & thalamus
Brain stem & spinal cord
Pituitary & hormones
Autonomic nervous system
Describe the pituitary gland
Small pea-sized structure, 0.5 grams in weight
Sits within a saddle-shaped depression of the sphenoid bone of the skull called pituitary fossa or “sella turcica” (Turkish saddle).
Connected to the hypothalamus via the pituitary stalk and via a blood vessel network (hypothalamo-hypophysial-portal system)
Composed of two distinct structures (anterior and posterior pituitary) that differ in embryological development and anatomy.
Describe the anatomy of the hypothalamus
Anatomically the hypothalamus is bound anteriorly by the optic chasm. These are nerves coming from the eyes on their way to the back of the brain. Laterally by the sulci, formed by the temporal lobe. And posteriorly by mammalian bodies.
Define pituitary stalk
The pituitary stalk descends from the central region from the hypothalamus and is termed infundibulum.
What is another name of the pituitary gland?
Hypophysis
What is another name of the anterior pituitary gland?
Adenohypophysis
What is another name of the posterior pituitary gland?
Neurohypophysis
How many parts does the anterior pituitary gland have?
3 parts
Name of parts of anterior pituitary gland
Pars Tuberalis - part of pituitary gland that surrounds infundibulum
Pars Intermedia - rudimentary in humans
Pars Distalis - anterior lobe of pituitary
How many parts does the posterior pituitary gland have?
2 parts
What are the name of the parts of the posterior pituitary gland?
The posterior pituitary consists of a Pars nervosa and infundibular stalk. Once again is connected to the pituitary, but still a distinct structure and has own set distinct hormones.
Cavernous Sinus
Cavernous sinus consists of arteries called carotid arteries which supply blood to the pituitary gland.
Embryology of Pituitary Gland
Anterior pituitary: derived from the ectoderm of Rathke’s pouch
Posterior pituitary: originates from downward extension of neural ectoderm from the floor of the diencephalon.
Where is growth hormone produced?
Growth hormone is produced from cells called somatotrophs in the pituitary.
When does production of growth hormone begin?
Now production of growth hormone begins early in foetal life and is continued throughout life.
What happens to the level of growth hormone as you age?
As you age, the level of growth hormones decreases (peak is at puberty).
How is growth hormone secretion regulated?
Growth hormone secretion is regulated by two hormones from the hypothalamus. One is the growth hormone releasing hormone, which stimulates growth hormone secretion and the other is somatostatin which inhibits secretion of growth hormone.
What stimulates the release of growth hormone?
From the peripheral stimulus such as stress, exercise, hypoglycaemia, malnourished or sepsis can stimulate the release of growth hormone.
What effects does growth hormone have?
Growth hormone has direct effects (does not stimulate other glands) but instead acts on bone, adipose tissue and muscles.
However, growth hormone also has its indirect effects through another hormone called IGF-1. The IGF-1 will be the main hormone which exerts the effects of growth hormone in peripheral tissue.
What does IGF-1 stand for?
Insulin-like growth factor
What is Insulin-like Growth factor (IGF-1)?
IGF-1 is a protein secreted from liver stimulated by growth hormone.
Most of the effects of growth hormone on peripheral tissue are mediated by IGF-1.
It has long half life and a stable marker to measure in blood sample unlike pulsatile secretion of growth hormone.
Clinical importance: plasma levels of IGF-1 in diagnosis of growth hormone abnormalities.
What is the function of growth hormone in children?
In children, predominant function is children growth.
What does growth hormone effect?
Carbohydrate Metabolism (Liver)
Bones
Lipid Metabolism (adipose tissue)
Muscles
How does growth hormone effect carbohydrate metabolism?
Carbohydrate Metabolism:
In Liver
Mediated by IGF-1
Increased gluconeogenesis
Increased glycogen synthesis
How does growth hormone effect bones?
It also acts on the bones as we know is primary function in children. It is essential for maintenance of bone mineralisation and causing anabolic bone effect by increases the bone formation markers.
How does growth hormone effect lipid metabolism?
In terms of lipid metabolism, it increases lipolysis and lipid oxidation and balances the adipose genesis (generation of adipose tissue) and lipolysis.
How does growth hormone effect muscles?
In muscle, there is reduced glucose uptake and increased protein synthesis.
What is Prolactin?
Prolactin is one such hormone produced in pituitary, has direct effects on target tissue, but does not necessarily stimulate on another gland in the periphery.
Prolactin is a lactation hormone - it stimulates breast to produce milk.
When are prolactin levels high?
Prolactin levels are higher in pregnancy and post childbirth preparing women for breastfeeding.
High prolactin levels will have negative effect on gonadotropin (sex hormones) making women infertile - this appears to be an in-built mechanism to stop women getting pregnant when breastfeeding.
Does prolactin have any releasing factors?
Unlike other hormones, there is no prolactin releasing factor coming from the hypothalamus.
Prolactin function in males
Prolactin has no major functions in males (current research suggests).
How is secretion of prolactin regulated?
The most important factor that regulates production of prolactin is a neurotransmitter called dopamine. This neurotransmitter is secreted from hypothalamus, travels through the pituitary stalk into the anterior pituitary and inhibits prolactin secretion.
What is the hypothalamic-pituitary-adrenal axis (HPA)?
A mechanism through which the hypothalamus, pituitary and adrenal glands form an axis and communicate with each other.
Describe the process of the hypothalamic-pituitary-adrenal axis (HPA)?
The hypothalamic hormone that increases the stimulation to the pituitary gland is called corticotrophin releasing hormone or CRH. This in turns stimulates a hormone called adrenocorticotrophic hormone (ACTH), and that in turns acts on the two adrenal glands situated above the kidney. The adrenal glands produce cortisol which is a glucocorticoid hormone. This cortisol when secreted in excess, has direct feedback to the anterior pituitary gland asking it to decrease adrenocorticotrophic hormone (ACTH) and direct feedback to the hypothalamus to decrease corticotrophin releasing hormone (CRH).
Functions of Cortisol
Maintains blood pressure, cardiovascular reactivity
Immunological and inflammatory responses
Cognitive function, memory, sleep, mood
Inhibits osteoblast function
Stimulates lipolysis, increases free fatty acids
Inhibits protein synthesis, increase protein breakdown
Gluconeogenesis, glycogenolysis
Increases GFR (glomerular filtration rate), water excretion
Describe the hypothalamic-pituitary-thyroid (HPT) axis
The regulation of thyroid hormone is through hypothalamic pituitary and thyroid axis. So, this hormone has similar principles to the cortisol hormone.
The hypothalamus releases a hormone called Thyrotropin releasing hormone which in turns stimulates the anterior pituitary gland to release TSH (thyrotropin stimulating hormone). This acts on thyroid tissue which releases two hormones called T3 and T4. These are two metabolites coming out of the thyroid gland, and are essential for body metabolism.
What are the thyroid hormone actions?
Heart - increased heart rate and cardiac output
Bone - increases bone turnover and resorption
GI - increased gut motility
Metabolic rate - body weight regulation
Promotes glucose uptake and increases lipolysis
Sympathetic nervous system: increased catecholamine (adrenaline) sensitivity
Describe the hypothalamic-pituitary-gonadal (HPG) axis in females
GNRH which is Gonadotropin releasing hormone, acts on the pituitary and releases two specific hormones known as Luteinizing hormone (LH) and follicle stimulating hormone (FSH) which then acts on ovaries and produce two essential hormones known as oestrogen and progesterone.
Function of hypothalamic-pituitary-Gonadal axis in females
Pubertal changes
Secondary sexual characters
Menstrual cycle
Follicular growth in ovaries
Ovulation
Fertility
Bone mineralisation
Describe the hypothalamic-pituitary-gonadal (HPG) axis in males
The hypothalamus Gonadotropin releasing hormone (GNRH) secretes LH and FSH which in turn secretes testosterone from the testicles and the testosterone is mainly driven by the luteinizing hormone from the Leydig cells of the testicles whereas the follicle stimulating hormone acts on different types of cells called Seritoli cells which then produce sperms. And these sperms are transferred into epididymis and then into the Vas Deferens in the sperm where in the sperm when ejaculated comes through this passage.
Function of hypothalamic-pituitary gonadal axis in males
Pubertal changes
Masculinity
Sexual Function
Libido (sexual desire)
Erectile Function
Spermatogenesis
Bone Mineralisation
What is the difference between the anterior and posterior pituitary gland?
Unlike the anterior gland, posterior pituitary gland is not composed of specific secretary cells and they themselves don’t release any hormones
Describe the posterior pituitary gland
The major component of this posterior pituitary gland is a collection of axon terminals which actually arise from two important nuclei in the hypothalamus called Supra Optic nuclei and paraventricular nuclei. The neurones from the nuclei travel through the pituitary stalk (infundibulum) into the posterior pituitary gland. Therefore, the hormones secreted in the hypothalamus are stored in posterior pituitary gland (vasopressin and oxytocin).
What two hormones are stored in the posterior pituitary gland?
Vasopressin and oxytocin
Other names of vasopressin
Arginine Vasopressin (AVP) or Vasopressin or Anti-Diuretic Hormone (ADH)
Describe Arginine Vasopressin (AVP)
Arginine Vasopressin (AVP) is at the level of the kidneys. Conserve body water and regulates overall volume status.
Secretion of AVP is regulated by stimuli from osmotic and fluid volume status and baroreceptors.
Reduction in body volume/fluid state increases plasma osmolality (blood viscosity) which activates hypothalamic osmoreceptors to stimulate AVP (Arginine Vasopressin) release.
Describe Oxytocin
Second hormone stored in the posterior pituitary gland. This has a role in child birth and lactation.
Stimulates myoepithelial contractions: in uterus during parturition.
Milk ejection from lactating mammary gland (suckling major stimulus for release).
