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HSM 330 (12)
Chapter 15

Chapter 15 notes

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Ryerson University
Health Services Management
HSM 330
Daolun Chen

Chapter 15: The Secretory Hypothalamus  The hypothalamus sits below the thalamus, along the walls of the third ventricle  This tiny cluster of nuclei makes up less than 1% of the brain’s mass An Overview of the Hypothalamus  Hypothalamus and dorsal thalamus are asdjacent  The hypothalamus integrates somatic and visceral responses in accordance with the needs of the brain  A tiny lesion can produce dramatic and often fatal disruptions  Homeostasis o In mammals, the requirement for life include a narrow range of body temperatures and blood compositions o The hypothalamus regulates these levels in response to a changing external environment  homeostasis  Structures and Connections of the Hypothalamus o The hypothalamus has three functional zones: lateral, medial, and periventricular o The lateral and medial zones have extensive connections with the brain stem and the telencephalon and regulate certain types of behaviour o The periventricular zone is so named because the cells of this region lie next to the wall of the third ventricle o One group of cells constitutes the suprachiasmatic nucleus (SCN) which lies just above the optic chiasm o These cells receive direct retinal innervations and function to synchronize circadian rhythms with the daily light- dark cycle o Other cells control the ANS, regulate the outflow of the sympathetic and parasympathetic innervations of the visceral organs o The cells in a third group, neurosecretory neurons, extend axons down toward the stalk of the pituitary gland Pathways to the Pituitary  The pituitary has two lobes, posterior and anterior  The hypothalamus controls the two lobes in different ways  Hypothalamic Control of the Posterior Pituitary o The largest of the hypothalamic neurosecretory cells, magnocellular neurosecretory cells, extend axons around the optic chiasm, down the stalk of the pituitary, and posterior lobe o Ernst and Berta Scharrer, proposed that these neurons release chemical substances directly into the capillaries of the posterior lobe o The Scharrers were correct. The substances released into the blood by neurons are neurohormones o The magnocellular neurosecretory cells release two neurohormones, oxytocin and vasopressin (peptides) o Oxytocin, released during the final stages of childbirth, causes the uterus to contract and facilitates the delivery of the newborn and also stimulates the ejection of milk o Information about a sensory stimulus—somatic, visual or auditory, reaches the cerebral cortex via the usual route, the thalamus, and the cortex ultimately stimulates the hypothalamus to trigger oxytocin release o Vasopressin (antidiuretic hormone – ADH) regulates blood volume and salt concentration o Changes are detected by pressure receptors int he cardiovascular system and salt concnetratoin-senstive cells in the hypothalamus o Vasopressin-containing neurons receive information and respond by releasing vasopressin which acts directly on the kidneys and leads to water retention and reduced urine production o Under conditions of lowered blood volume and pressure, communication between the brain and the kidneys actually occurs in both directions  The kidneys secrete an enzyme into the blood called renin  This sets off a sequence of biochemical reactions in the blood  Angiotensinogen, released from the liver, is converted by renin to angiotensin I which breaks down
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