Lecture 16: Hypothalamus, Pituitary Gland, and Pineal Gland Flashcards
What is unique about the Hypothalamus, Pituitary Gland and Pineal gland?
All of the structures are midline and there is only one of each
What is the main function of the hypothalamus?
To maintain homeostasis
How does the hypothalamus maintain homeostasis?
By regulating ANS (ascending and descending tract)
What do the ANS ascending and descending tracts regulated by the hypothalamus do?
Control body temperature, hunger, thirst, fatigue, sleep and circadian cycles
What does the hypothalamus link togehter?
The nervous system to the endocrine system
What links the nervous system to the endocrine system?
The hypothalamus
Through what does the hypothalamus link the nervous system to the endocrine system?
Via the pituitary gland
How does the hypothalamus link the nervous and endocrine system via the pituitary gland?
By secreting neurohormones that stimulate or inhibit secretions of the pituitary gland
What does the hypothalamus synthesize and secrete?
Neurohormones
What are the five main categories of inputs to the hypothalamus?
- Nucleus of the solitary tract
- Reticular formation
- Retina
- Amygdala, hippocampus and the olfactory cortex
- Intrinsic hypothalamic receptors
What kind of inputs does the nucleus of the solitary tract send to the hypothalamus?
Visceral sensory information from the glossopharyngeal nerve (blood pressure) and vagus information (gut distension?
Where does the hypothalamus receive: Visceral sensory information from the glossopharyngeal nerve (blood pressure) and vagus information (gut distension) from?
The nucleus of the solitary tract
What kind of inputs does the reticular formation send to the hypothalamus?
Inputs from the spinal cord including information about skin temperature which is relayed to the hypothalamus
What kind of inputs does the Retina send to the Hypothalamus?
Some fibers from the optic nerve go directly to the suprachiasmatic nucleus to regulate circadian rhythm
Where does the hypothalamus receive Inputs from the spinal cord including information about skin temperature which is relayed to the hypothalamus?
The Reticular formation
Where does the hypothalamus receive information about light/dark to regulate circadian rhythms?
The retina
What kinds of inputs do the Amygdala, hippocampus and the olfactory cortex send to the hypothalamus?
Inputs that help to regulate behaviours such as eating and reproduction
Where does the hypothalamus receive inputs to control behaviour like eating and reproduction?
The amygdala, hypothalamus and olfactory cortex
What do the intrinsic receptors of the hypothalamus regulate?
Thermoreceptors, osmoreceptors that measure temperature and ionic balance
How can the hypothalamus be involved in HR regulation?
- The NTS can sample blood oxygen and co2 concentration from the heart and send this information to the hypothalamus
- In response the hypothalamus can send outputs via the DMNV to alter heart rate
Where do autonomic afferents project back to and for what?
The hypothalamus instead of the thalamus for regular senssation
What projects back to the hypothalamus instead of the thalamus?
Autonomic afferents
What happens after autonomic afferent project back to the hypothalamus instead of the thalamus?
The hypothalamus then projects outward and has an effect that is not under conscious control
What are the two main nuclei of the hypothalamic limbic system?
- Lateral Hypothalamic nuclei
- Ventromedial nucleus
What are the lateral hypothalamic nuclei and the ventromedial nuclei apart of?
The Hypothalamic limbic system
What is the Lateral hypothalamic nuclei transversed by?
Longitudinally by many fibres including the medial forebrain bundle
What does the medial forebrain bundle traverse?
The lateral hypothalamic nuclei
What is lateral hypothalamic area important for?
The control of food and fluid intake (desire to eat)
What controls the desire to eat?
The lateral hypothalamic nuclei
What do lesions to the hypothalamic nuclei cause?
Aphagia and adipsia
What is the ventromedial nucleus involved in?
The control of food and fluid intake
What controls the desire to stop eating?
The ventromedial nucleus
What do lesions to the ventromedial nucleus cause?
Abnormally increased food intake
What are the three main hypothalamic efferents?
- Pituitary gland
- Autonomic nervous system
- Limbic system
What is the endocrine section of the hypothalamic efferents?
The pituitary gland
What is the autonomic nervous system portion of hypothalamic efferents?
The vagus nerve
What structures are part of the limbic system hypothalamic efferents?
The amygdala and the hippocampus
How does the hypothalamus use the pituitary as an efferent?
The hypothalamus has control over hormone production (anterior lobe) or hormone release (posterior lobe) of the pituitary gland
What does the hypothalamus use the autonomic nervous system for as an efferent?
To control internal organs
What does the hypothalamus use the limbic system for in terms of efferents?
The hypothalamus initiates appropriate instinctual motor behavior repertoires (such as feeding)
What unites at the hypothalamus?
The autonomic and endocrine systems
What are the superior structures of the brain?
The cerebrum, thalamus and hypothalamus
What are the lower structures of the brain?
Midbrain, pons and cerebellum
What is the middle strucutres of the brain?
The hypothalamus which projects to the pituitary
What are the two parts of the pituitary?
The Adenohypophysis (anterior)
The Neurohypophysis (posterior)
What kind of gland is the pituitary?
An endocrine gland or a neuroendocrine gland
What is the hormone producing part of the pituitary?
The Adenohypophysis
What is the hormone releasing part if the pituitary?
The neurohypophysis
What is the Median eminence?
The projection of the hypothalamus to the posterior pituitary
What is the infundibulum?
The connection of the pituitary to the hypothalamus
What is the pituitary protected by?
Bone and surrounded by the hypophyseal fossa
What does the hypophyseal fossa surround?
The pituitary gland
What hormones are released by the anterior pituitary?
- TSH
- ACTH
- FSH and LH
- Growth Hormone (GH)
- Prolactin (PRL)
- Endorphins
What part of the pituitary releases:
- TSH
- ACTH
- FSH and LH
- Growth Hormone (GH)
- Prolactin (PRL)
- Endorphins
The anterior pituitary
What does the posterior pituitary release?
- Oxytocin
- ADH
What part of the pituitary releases oxytocin and ADH?
The posterior pituitary
What are the two nuclei of the medial hypothalamus?
- Paraventricular nucleus (PVN)
- Supraoptic nucleus (SON)
What does the Paraventricular nucleus do?
Synthesized Oxytocin and releases it in the posterior pituitary
What nucleus in the hypothalamus synthesizes oxytocin?
The Paraventricular nucleus
What is activation of the paraventricular nucleus cuased by?
The release of hormones induced by suckling
What does oxytocin do in females?
Stimulates milk production by the mammary gland and causes contraction of uterine muscle
What stimulates milk production by the mammary gland and causes contraction of the uterine muscle?
Oxytocin from the paraventricular nucleus
What is the breakdown of the meaning of oxytocin?
oxy = swift; tocin = birth
What does oxytocin do in males?
Causes smooth muscle contractions in the prostate
What causes smooth muscle contractions in the prostate?
Oxytocin
What does the Supraoptic nucleus do?
Produces antidiuretic hormone and releases it in the posterior pituitary
Where is antidiuretic hormone produced?
In the Supraoptic nucleus
When is antidiuretic hormone released?
During an increase in osmolarity
Where is the increase in osmolarity that causes antidiuretic hormone to be released sensed?
In osmosensitive neurons in the supraoptic nucleus
What is antidiuretic hormone (ADH) released in response to?
A rise in electrolytes of fall in blood pressure of blood volume
What does Antidiuretic hormone do?
- It acts on the kidneys to increase water absorption to maintain water homeostasis
- Causes constriction of the peripheral blood vessels to increase blood pressure
What can the release of ADH be inhibited by?
Coffee or alcohol
What happens if the release of ADH is inhibited by coffee or alcohol?
Water will not be reabsorbed and body will produce dilute urine
How will a lesion to the medial hypothalamus affect ADH?
It will affect the production of ADH
What would happen if ADH is not produced?
A person will be thirsty because they are continuously losing liquid in the urine
What will happen if too much ADH is produced?
A person will drink too much and suffer from water intoxication causing electrolytes in the blood to be diluted
What is important about the production of Oxytocin and ADH?
Both oxytocin and ADH are produced by the hypothalamus and carries them to the posterior pituitary
How are Oxytocin and ADH brought from the hypothalamus to the posterior pituitary?
They are brought in granules through the Hypothalamo-hypophyseal tract
What does the hypothalamo-hypophyseal tract do?
Carries oxytocin and ADH produced by the hypothalamus to the posterior pituitary
What do the Supraoptic nuclei and paraventricular nuclei do?
Manufacture ADH and oxytocin released by synaptic terminals at capillaries in the posterior lobe of the pituitary gland
What is the Hypophyseal portal system?
- The capillary networks in the median eminence are supplied by the hypophyseal artery
- Before leaving the hypothalamus, the capillary networks unite to form a series of larger vessels that spiral around the infundibulum to reach the anterior lobe
- Arterial blood from the hypothalamus area drain into the anterior pituitary to stimulate the anterior pituitary to produce hormones
How does the hypothalamus have a relationship with the anterior pituitary?
Through the portal system
What is the orchestrator of the endocrine system?
The anterior pituitary
What does thyroid stimulating hormone released by the anterior pituitary do?
Stimulates the activity of the thyroid
What does Adrenocorticotropin hormone released by the thyroid do?
Stimulates the activity of the adrenals
What does follicle stimulating hormone released by the anterior pituitary do?
Regulate gonadal function and reproductive cycle
What does Lutenizing hormone released by the anterior pituitary do?
Regulate gonadal function and reproductive cycle
What does Prolactin released by the anterior pituitary do?
Stimulate lactation and development of mammary glands
What do endorphins released by the anterior pituitary do?
Control of pain and nociceptive signals
How does Cortisol affect blood sugar?
It raised blood sugar by preventing insulin function and promoting gluconeogenesis
What is cushing syndrome?
Too much cortisol production
What disease is characterized by too much cortisol production?
Cushing’s disease
What can tumors to the hypothalamus and pituitary glands do?
Lead to underproduction or overproduction of circulating hormones
What are the disorders of growth?
Dwarfism, gigantism and acromegaly
What are the disorders of sexual function?
Precocious puberty and hypogonadism
What are disorders of body water control?
Diabetes insipidus and pathological drinking
What is diabetes insipidus?
Losing to much water
What is pathological drinking?
Drinking too much water
What are disorders of eating?
Obesity and bulimia
What are disorders of adrenal cortical control?
Cushing’s disease and adrenal insufficiency
How does the hypothalamus affect growth hormone?
The hypothalamus maintains homeostatic levels of GH
How does GH affect cells?
Cells under the action of GH increase in size (hypertrophy) and number (hyperplasia)
How does GH affect bones?
GH causes an increase in bone length and thickness by deposition of cartilage at the ends of bones
How do sex hormones affect bones?
During adolescence, sex hormones cause replacement of cartilage by bone, halting further bone growth even though GH is still present
What can too little growth hormone cause?
Gigantism
What can too little GH cause?
Dwarfism
What is Gigantism?
Excess GH before puberty
What causes dwarfism?
hGH deficiency before puberty
What causes Acromegaly?
Excess hGH after puberty
What is the difference between Gigantism and Acromegaly?
- Gigantism is when there is excess growth hormone before puberty
- Acromegaly is when there is excess growth hormone after puberty
What happens in gigantism?
Excess hGH before puberty causes excessive length of bones, coarsening of the facial bone, slowed sexual development and mental slowness
What happens in acromegaly?
Excess hGH after puberty causes thickening and coarsening of bones, enlargement of lips, nose, jaw and thickening of tongue of skin. Bones also thicken
What vision loss can a pituitary tumor cost?
Bitemporal hemianopsia
How can a pituitary tumor cause bitemporal hemianopsia?
It can compress the optic chiasm
How does bitemporal hemianopsia affect the visual field?
It causes tunnel vision. So you are unable to see the peripheral visual fields
What is the mechanism behind bitemporal hemianopsia?
The axons from the midline that see the peripheral visual fields usually cross over at the optic chiasm, but because it is compressed people are no longer able to see
What is the Transsphenoidal approach to removing pituitary tumors?
Entering through the nasal cavity and drilling through the sella turcica
What is the Epiphysis?
The pineal gland
What is another name for the pineal gland?
The epyphsis
What does the Pineal gland sit in close proximity to?
The aqueduct of the 3rd and 4th ventricle
What is the main function of the Pineal Gland?
To produce melatonin in the absence of light stimulation
What nuclei do retinal axons project to?
The suprachiasmatic nuclei (SCN) of the hypothalamus
What is the Retinohypothalamic tract?
The pathway that the retinal axons project to the suprachiasmatic nuclei when there is light stimulation
What happens after light stimulates the retina and it travels to the SCN?
Nerve impulses originate from the SCN via the sympathetic nervous system and travel to the pineal gland to inhibit the production of melatonin
How is the production of melatonin inhibited in the pineal gland?
Retinal axons sense light and project to the suprachiasmatic nucleus. The suprachiasmatic nucleus then sends nerve impulses via the sympathetic nervous system which travels to the pineal gland to inhibit melatonin production
When do impulses from the SCN on the pineal gland stop?
At night when there is no light to stimulate the hypothalamus
What does the SCN do in terms of circadian rhythms?
It serves as a clock that regulates brain and endocrine systems
What are the Circadian Rhythms controlled by?
Endogenously: Clock genes
Exogenously: Light regulation and environment
