Homeostasis

Homeostasis Definition

Regulation definition

Homeostasis - The process by which the body maintains a constant internal environment

Regulation – responding to fluctuations around a set point

• In animals: use nerves, hormones and hypothalamus

• In plants: achieved through hormones

Importance of homeostasis

Required to keep our cells and enzymes functioning

• Many reactions inside the body only work in certain conditions, regardless of a changing outside environment

• Each variable in the body needs to be kept within a tolerance limit for the body to function

  • Tolerance limit – range of acceptable deviation

  • Inside tolerance limits = reactions proceed normally

  • Outside tolerance limits = reactions are impaired = negative consequences on health of organism

  • E.g. optimal digestion in the stomach occurs at a pH of 2. Any higher pH = enzymes cannot break down food as efficiently

e.g. of homeostasis

• Blood pH levels

• Blood glucose

• Internal body temperature

• Water availability

The Stimulus and Response Model

The body’s way of detecting an internal / external change in the environment and react accordingly

1. Stimulus - Something happens that causes a change in the environment

2. Receptor - Recognises and respond to stimulus, by sending a message the CNS

   1. Thermoreceptors – detect changes in temperature

   2. Chemoreceptors – detect the presence of particular chemicals

   3. Mechanoreceptors

   4. Photoreceptors – light receptors

   5. Nociceptors – pain receptors

3. Control Centre - Information from sensory receptors is compared to expected levels

   1. Normally the central nervous system (CNS) in animals  Brain and spinal cord

   2. Figures out how to respond appropriately and then sends a message to the effector

4. Effector - Enacts homeostatic response → Fixes the imbalance

   1. Muscles (expand or contract) → Nervous system - Electrical impulse sent along nerve cells

   2. Glands (release secretion) → Endocrine system - Uses hormones to act as chemical messengers sent through the blond

5. Response - Action body takes to restore balance

   1. Scale of the response depends on

      1. Sensitivity of receptor

      2. Tolerance of CNS

      3. Efficiency of effector

Feedback loops

Positive	Negative
When a variable triggers an amplifying response More, more, more! The response encourages the stimulus	When a variable triggers a counteractive response Stop, stop, stop! The response reverses the stimulus Brings the body back to the desired state
e.g. Pregnancy In the late stages of pregnancy, when the baby’s head touches the cervix, it dilates, which causes oxytocin to be released to further the dilation occurring. This happens in a cycle to push the baby out.	e.g. Thermoregulation temp increases → thermoreceptors → hypothalamus → muscular skeletal system, blood vessels →metabolism decrease, sweat, vascodilation → temp goes down e.g. Glucose levels in blood levels rise → sensor cells in pancreas → pancreas beta cells → liver, muscle and fat cells take in mroe glucose, muscle/liver converts it to glycogen

Thermoregulation

internal regulation of an animal’s body temperature

Body temperature – most optimal temperature for reaction in organism to occur

• 37 in humans

• ensures all chemical reactions occur at the optimal temperature → highest rate of reaction → body works the most efficiently

Endo vs Ectotherms

Endotherms	Ectotherms
Warm-blooded Create heat by adjusting processes in our body Rely on our own physiological sources of heat to regulate temperature → regulate temp internally Still absorb / release heat in many ways (e.g. conduction), but we can manipulate our inside temperature better	Cold-blooded Cannot generate heat themselves Rely on external sources of temperature to heat up or cool down → rely on environment Depend solely on environment
e.g. Dogs, elephants, humans	e.g. Lizards

Process of thermoregulation

stimulus	increase / decrease in body temp
receptor	Thermoreceptors in skin Detect external changes in temperature Triggered more frequently Thermoreceptors in the hypothalamus Cluster of temperature-sensitive cells Monitor the body’s internal temperature by measuring blood temperature
control centre	Nervous system: Receptors send messages to the hypothalamus Receives all information about temperature via motor neurons Sends out electrical messages to activate a certain physiological response to achieve balance Endocrine System: Thyroid stimulating hormone (TSH) Thyrotropin releasing hormone (TRH) released by hypothalamus → thyroid stimulating hormone (TSH) by pituitary gland → thyroid to release of T3 and T4. Hypothalamus sends out thyrotropin-releasing hormone (TRH) Causes the pituitary gland to secrete TSH Acts on the thyroid gland to release thyroid hormones (e.g. T3, T4) to regulate metabolic processes → thus regulates heat generated
effector	Muscles, blood vessels, cells
response	Responding to Decrease in Temp Piloerection – hairs standing erect on the skin (goosebumps) → Trap air close to the skin to prevent heat loss by convection Vasoconstriction – blood vessels constrict so less blood travels to the surface of skin → Less heat is lost from blood Shivering – muscles cells performing respiration (Breaking down glucose to make energy → Respiration releases heat) Increasing metabolism – main source of heat when the body is at rest → influenced by Endocrine system Non-shivering thermogenesis – breaking down of brown fat to release heat Responding to increase in temp Vasodilation – blood vessels dilate → Blood actively loses heat to external environment Sweating - the release of liquid from the body's eccrine and apocrine glands → Draws heat to skin to evaporate from sweat Decreasing metabolism – hypothalamus reduces the rate of cellular respiration

Glucose Homeostasis

stability in the levels of glucose in the blood (BGLs)

• Levels rise after eating dinner

• Fall after having done exercise or not eating for a while

• If it moves out of the tolerance limit, a homeostatic response is triggered

  • 3.5-8 millimole per litre (mmol/L)

• Excess glucose is stored as glycogen (polysaccharide form  can be broken back down into glucose monosaccharide)

• Glycogen is stored inside of liver and skeletal muscle cells

Importune of glucose / glucose homeostasis

• When food gets broken down it releases glucose

• Glucose is absorbed by small intestines and released into bloodstream

• It is dispersed through body and taken up by cells

• Used in respiration to make ATP for energy

• Powers cellular functions (e.g. DNA replication, protein synthesis, etc…)

• Keeps body’s tissues working properly

Process of glucose regulation

Stimulus	Blood glucose levels fall below the tolerance limit	Blood glucose levels rise above the tolerance limit
receptor	Sensor cells in pancreas sense BGLs dropping below 5 mmol/L	Sensor cells in pancreas sense spike in BGLs above tolerance limit
control centre	Endocrine system: Alpha cells in Pancreas Releases hormone called glucagon + adrenal gland produces cortisol → proteins break down into glucose → ensures enough glucose in blood for fight/flight response	Endocrine system: Beta cells in Pancreas Releases hormone called insulin
effector	Target tissues are the liver and skeletal muscle cells	Target tissues are fat, liver and skeletal muscle cells
response	Liver binds to glucagon and triggers an enzyme reaction that breaks down glycogen into glucose Glucose is released into the bloodstream	Stimulates liver, fat and muscle cells to increase their uptake of glucose Liver converts glucose into glycogen → Excess glucose is stored as fat

Endotherms → behavioural, structural and physiological adaptations in endotherms that assist in maintaining homeostasis

Adaptations – characteristic that increases an organism’s chance of survival and reproduction in its environment

• Caused by natural selection → NOT chosen by organism, but rather a produce of mutations and selection pressures

• Behavioural = way the organism acts

• Structural = physical characteristics

• Physiological = the way the body functions

The Nervous System role

a system that allows organisms to take in and respond to information from the environment by passing electro-chemical messages through a network of neural pathways

• Takes messages from receptors and interprets the correct response to the information

• Sends messages to effectors to respond to the stimulus

• Messages are carried as nerve impulses along neurons (nerve cells)

Structure of neurons and their function

Neurons – functional units of the nervous system that carry signals around the body

General structure

B DAMS 1. Dendrites – receive the neurotransmitter (signal containing information) from other neurons → Large surface area = increase information received 2. Cell Body - interpret the neurotransmitter and if it is strong enough, it is sent sends to the axon → Contains the nucleus 3. Axon – carries the signal (called an action potential at this stage) to the synaptic knobs 4. Myelin sheath – insulates the axons 5. Synaptic knobs – release the action potential as a neurotransmitter to be received by other cells → Connects neuron to the next cell

types of neurons

Components of the nervous system

• CNS

  • brain

  • spinal cord

• PNS → neurons

  • somatic nervous system

  • autonomiuc NS

    • sypathetic and parasympathetic

central nervous system

Includes the brain and spinal cord

• Gather information from the body and coordinates responses

Brain - serves as the primary processing centre

• Forebrain

  • Cerebrum - memory, and voluntary movement

  • Thalamus – receives sensory information from body

  • Hypothalamus - regulates body temperature, hunger, emotions, hormones release from pituitary gland

• Mid brain - controls reflex movements of eye muscle, head and neck

• Hindbrain

  • Cerebellum - controls and coordinates muscular activity

  • Medulla oblongata - controls involuntary actions

Spine - Sends motor commands from the brain to the peripheral body and relay sensory information from the sensory organs to the brain

Peripheral nervous system

Neurons that connect the CNS to the rest of the body

• Path that carries messages towards and away from CNS

Somatic Nervous System

The voluntary, conscious part of the nervous system

• Nerves connected to skin, sensory organs, skeletal muscles

• Processes information that arrives from external stimuli (five senses)

• Controls skeletal muscles to allow for voluntary movement

Autonomic Nervous System

The involuntary, unconscious part of the nervous system

• Nerves connected to cardiac muscle, smooth muscle in organs

• Controls heart rate, digestion, salivation, sweating, pupil diameter, etc…

• Involves parasympathetic and sympathetic nervous system

parasympathetic (rest and digest)	sympathetic (fight or flight)
Stimuli: When you are relaxed/calm Control centre: Nervous system recognises you are not in danger Relaxes body Acetylcholine is released Effectors and Responses Heart slows to normal beating Digestive system continues to digest food, breathing normally Body is normal	Stimuli: When you are stressed Control centre: Nervous system believes you are in danger Prepares for action Adrenaline is released Effectors and Responses Heart starts pumping faster so that muscles have more oxygen Digestion stops so energy is focused on survival Non-shivering thermogenesis

The Endocrine System overview

a group of glands that secrete hormones

Glands – a group of specialised, hormone-secreting cells

Hormone – chemical messengers that cause a response in another region of the body

e.g. insulin is a hormone that acts on liver, muscles and fat cells to maintain glucose levels

• Different hormones are produced by different glands

• Each hormone binds to specific receptors found on target cells

  • Target tissues – tissues that contain target cells, intended destination of hormone

  • Hormones can have effects on tissue widely distributed throughout the body

  • A tissue just needs a hormone receptor to enact a response

• Transported in the circulatory and lymphatic systems

  • Hormones are diffused out of glands into blood to be takes around by circulatory system

  • Blood is pumped through blood vessels

• Relay messages from the receptor to the control centre to the effector, and used by the effector to make a response

how endocrine system works

Regulated by the stimulus-response model  releases hormones in response to certain stimuli

1. Stimuli cause endocrine glands to make and release hormones

   1. Neural stimuli – receiving nerve impulses

   2. Hormonal stimuli – detecting change in the concentration of hormone

   3. Humoral stimuli - detecting change in the concentration of a substance in the blood

2. Once hormone is released, it binds to its target cell to ensure a response

   1. If the cell has more receptors = more dramatic response

Endocrine Glands and Hormones

Endocrine Gland	Hormone
Hypothalamus (brain)	Gonadotropin-releasing hormone (GnRH) to trigger pituitary gland to make FSH and LH for ovulation Releases TRH Produces antidiuretic hormone (ADH)→ increases water absorption in the blood from the kidneys → concentrated urine → osmoregulation (water regulation)
Pituitary gland (brain)	Posterior pituitary gland • Stores and secretes ADH Anterior pituitary gland • Producers of TSH, growth hormone, FSH, LH
Pineal gland (brain)	melatonin for sleep
Thyroid gland (neck)	T3 and T4 involved in thermoregulation by increasing metabolism
Thymus gland	thymosin to stimulate the development of T cells
Pancreas (behind stomach)	glucagon and insulin
Adrenal glands	aldosterone, adrenaline and noradrenaline → Controls blood pressure and fight or flight response
Gonad glands	ovaries → oestrogen and testosterone testes → testosterone

Endocrine vs Nervous system

thermoregulation vs glucose regulation

Osmoregulation in plants definition

internal regulation of a plant’s water and salt levels

• Maintains salt and water concentration → since salt controls osmosis and moves water

• Plants need water to be turgid (full vacuole)  helps them stand up straight

• Water dissolves minerals and allows them to be transported around the plant

• Water needed for photosynthesis

osmoregulation: dry environments

Mesophytes: plants adapted to live in moderately wet environments (e.g. corn, roses)

• close the stomata (pores on the underside of the leaf that faciliate gas exchange) by decreasing the amount of water in guard cells

  • Controlled by abscisic acid (hormone)

  • Generally, close their stomata when it is hottest (e.g. midday) and leave them open at other times

  • Allows leaf to maximise photosynthesis and minimise water loss

• Waxy Cuticle → A waterproof barrier that reduces water loss

• Vacuoles → store water + keep plant cell turgid (stand up)

Xerophytes: Plants that are specifically adapted to live in arid regions (e.g. cactus, eucalyptus tree)

• Reduced number of stomata in leaves → Less stomata = less water vapour lost from transpiration

• Drooping leaves, Sunken stomata, Hair on leaves

  • Traps air around the stomata

  • Air becomes saturated with water vapour

  • Creates a humid microclimate

  • Means less water is transpired

osmoregulation: wet environments

Hydrophytes: plants adapted to wet environments (e.g. waterlily)

• Increased number of stomata

  • More stomata = optimised gas exchange = more transpiration

• Large and flat leaves

  • Large surface area to volume ratio

  • Further promotes water loss (more area for transpiration to occur)

osmoregulation: salty environments

Halophytes: plants that can survive in saline environments

Due to osmosis – the movement of water from high to low water concentration across a semipermeable membrane

• Water will move from less salty to salty environments to maintain balance

• For plants submerged in salt water (e.g. mangroves)

  • Water within roots (needed by plant) is more likely to move of the plant into the soil

  • Makes it harder for the plant to absorb water from the soil

  • Excess salt concentration can be toxic

Salt exclusion

• Special tissues in the roots stop salt from entering the plant but allow for water uptake

e.g. grey and red mangroves

Salt excretion

• Plant actively concentrates salt and excretes it through special glands on leaves

• Salt is crystalised on surface to be washed or blown away

e.g. grey and river mangroves

Salt accumulation

• Plant deposits salt in older tissue (e.g. old leaves)

• These tissues are shed to remove salt

e.g. milky mangrove

Define action potential

Action Potential – electrical signals generated by excitable cells

• Can be sent to neighbouring cells

• Excitable cells – generates electrical signals from a stimulus (e.g. neurons, muscle cells)

define membrane potential

Membrane potential – difference between electrical potential inside and outside the cell

• You compare charge inside and outside of cell

• Negative charge/voltage = polarised

• Positive charge/voltage = depolarised

Types of neurons

Sensory neurons	Carry electrical impulses from receptors to the CNS Information received has a long way to travel Long dendrites to receive information from receptors
Motor neurons	Carry electrical impulses from the CNS to effectors Conveys commands to muscles, organs and glands Long axons to send sensory information to effector cells
Interneurons / relay neurons	Transmit electrical impulses between neurons Link up sensory and motor neurons Found exclusively in CNS Short dendrites and short axons

describe how neural pathways work

Neural Pathways - connections between neurons that allow signals to travel from one area to another