BIOL125 Lecture Notes - Lecture 2: Integumentary System, Medulla Oblongata, Cerebral Cortex
8 Jun 2018
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Homeostasis
• 1.5. What is homeostasis?
o Homeo = unchanging, stasis = standing
o Refers to maintenance of a stable, optimal internal body environment
o Two general mechanisms
• Autoregulation (intrinsic regulation)
▪ Individual cells can maintain their own homeostasis
• Extrinsic regulation (nervous and/or endocrine system)
o 1.5.1. its importance in the human body
• Loss of homeostasis -> cell injury -> disease or death
o 1.5.2. its processes
• 1.5.2.1. stimulus
▪ Receptor - a sensor that detects changes (stimuli) in the body's
environment
• Thermoreceptors (heat and cold) in skin
• Touch receptors (fine touch and pressure) in skin
• Baroreceptors in arterial walls that detect stretch on walls
• Chemoreceptors that detect CO2, O2 and pH changes
• Proprioceptors send information about joints back to the CNS
• 1.5.2.2. monitoring
▪ The control/integration centre - monitors incoming information from
receptor -> processes -> sends commands to restore homeostasis
• 1.5.2.3. response
▪ Effector - cell or organ that responds to the command centre
• Muscle cells (skeletal, smooth, cardiac)
• Glands (e.g. thyroid or parathyroid cells)
• Kidney cells
• Adipose tissue
• Alpha and beta pancreatic cells
▪ Actions taken by cells either:
• Negates change away from homeostasis - opposes stimulus
direction (negative feedback)
• Enhances/increases stimulus direction (positive feedback)
• 1.6. An overview of the systems and mechanisms that regulate and maintain homeostasis
o Control centre
• Autoregulation
▪ A cell, tissue, organ or organ system automatically adjusts its activities
in response to an environmental change to maintain
balance/equilibrium
▪ May involve same cells being sensor, control centre and effector
▪ e.g. alpha and beta cells in pancreas monitor changes in blood glucose
level (BGL) via glucokinase enzyme -> alpha or beta cells secrete
hormone in response (insulin or glucagon)
▪ O2 levels drop in a tissue -> local cells release chemical (NO) to dilate
local blood vessels -> increased blood flow -> increased O2 doe tissues
• Extrinsic regulation
▪ Nervous or endocrine system adjusts activities of several systems at
once to maintain homeostasis
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▪ Involves a brain centre such as the hypothalamus e.g. body temperature
regulation, or medulla oblongata e.g. respiration rate increased if CO2
builds up or O2 levels drop
▪ When exercising:
• NS sends signals to increase heart rate and force of contraction
• Increases depth and rate of breathing to reduce blood flow to less
active systems e.g. digestive and renal
• Redirects it to muscles, heart and lungs, to increase heat loss from
skin
▪ Thermoregulation:
• ANS activates other brain centres -> lethargy or conscious activity
• Muscular system -> shivering
• Integumentary system -> sweating
• Cardiovascular system -> blood flow changes in skin
• Increased/decreased release of thyroid hormone to
increase/decrease cell BMR, ATP production and therefore heat
production
• Piloerection is where the hairs stand up in attempt to trap air to
become warmer
o Roles of the Nervous and Endocrine System
• Nervous
▪ Rapid, short term and very specific responses
▪ e.g. hand on hot plate -> rapid contraction of skeletal muscles to pull
hand away from heat
• Endocrine
▪ Longer-term changes which persist for days or weeks via release of
hormones
▪ e.g. long-term regulation of blood volume and composition via
hormones Renin, Aldosterone and ADH
▪ An short term responses, e/g/ release of adrenaline and noradrenaline
o Role of skeletal muscle in thermoregulation
• Thermoregulation
▪ Involves autonomic regulation by hypothalamus (and medulla
oblongata) e.g. blood flow to skin increased/decreased,
sweating/shivering and conscious (cerebral cortex) activity
▪ Conscious - add or remove clothes, drink cold water or hot drinks, sit by
a heater or fan
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Document Summary
What is homeostasis: homeo = unchanging, stasis = standing, refers to maintenance of a stable, optimal internal body environment, two general mechanisms, autoregulation (intrinsic regulation) Individual cells can maintain their own homeostasis: extrinsic regulation (nervous and/or endocrine system, 1. 5. 1. its importance in the human body. Increases depth and rate of breathing to reduce blood flow to less active systems e. g. digestive and renal: redirects it to muscles, heart and lungs, to increase heat loss from skin, thermoregulation: Integumentary system -> sweating: ans activates other brain centres -> lethargy or conscious activity, muscular system -> shivering, cardiovascular system -> blood flow changes in skin. Set point/range determined by data from 95% of large sample population: 95% of healthy adults have a body temperature range between 36. 7-37. 2 c. Individual variability to be taken into account when determining if body temperature change is related to disease presences or not: 1. 7.
