Biology Lecture on Homeostasis and Human Physiology

Jun 5, 2024

Biology Lecture on Homeostasis and Human Physiology

Introduction

  • Presented by Lauren, Head of Biology
  • AQA Paper 2 Explanation
  • Resources available: flashcards, predicted papers, detailed walkthroughs

Homeostasis

  • Regulation of internal environment conditions
  • Maintains body temperature (~37°C), blood glucose, and water levels
  • Ensures proper function of cells and enzymes
  • Controlled by the nervous and endocrine systems

Process of Homeostasis

  1. Detection: Receptors in organs detect internal or external environmental changes (stimuli).
  2. Information Relay: Transmitted via hormones or nervous impulses to coordinators (brain/spinal cord or pancreas).
  3. Coordination: Processed by coordinators, which send out responses via hormones or nervous impulses.
  4. Response: Effectors (glands or muscles) initiate responses to the stimuli.

Nervous System

  • Central Nervous System (CNS): Brain and spinal cord
  • Nerves: Bundles of nerve cells that transmit electrical impulses
  • Function: Allow humans to react to surroundings and coordinate responses

Sequence of Nervous Response

  1. Stimulus detected by receptors (e.g., eyes, skin, nose).
  2. Receptors send impulses to the CNS.
  3. CNS sends impulses to effectors (muscles/glands).
  4. Effectors cause a response (muscle contraction or hormone release).

Reflex Actions

  • Unconscious and quick responses to stimuli
  • Involve only three neurons: sensory, relay, and motor neurons
  • Examples: knee jerk response, pupil response to light, reflex to pain

Reflex Arc Explanation

  1. Stimulus (e.g., pain) detected by a receptor in the skin
  2. Impulses travel via sensory neuron to the spinal cord (relay neuron)
  3. Relay Neuron sends impulse to motor neuron
  4. Motor Neuron sends impulse to muscle causing contraction
  5. Synapse: Chemical released between neurons to propagate impulse

Measuring Reaction Time

  • Ruler Drop Test: Measure time to catch a falling ruler
  • Distance converted to reaction time using a table
  • Variables affecting reaction time: practice, sleep, caffeine, distractions
  • Controlled experiment factors: mass of the ruler, randomness of drop

The Brain

  • Cerebral Cortex: Controls conscious thoughts, language, memory
  • Cerebellum: Coordinates muscle contractions and balance
  • Medulla Oblongata: Controls unconscious functions like heart rate and breathing rate
  • Brain Study Methods: Injury observation, electrical stimulation (EEG), MRI scans
  • Brain Disorders Treatment: Ethical considerations, complexity in treatment and diagnosis

The Eye

  • Detects light intensity and color
  • Parts:
    • Retina: Contains rods and cones (light receptors)
    • Iris: Muscles controlling light entry
    • Cornea: Focuses light
    • Ciliary Muscles & Suspensory Ligaments: Adjust lens shape for focusing

Eye Functions

  • Bright Light: Circular iris muscles contract; radial muscles relax
  • Dim Light: Circular muscles relax; radial muscles contract
  • Accommodation: Adjusting lens for near and far objects

Vision Defects

  • Hyperopia: Long-sightedness (fixed with convex lenses)
  • Myopia: Short-sightedness (fixed with concave lenses)
  • Cataracts: Cloudy lens replaced surgically

Temperature Control

  • Thermoregulatory Center in the Brain: Detects body temperature
  • Cold Response: Vasoconstriction, shivering, hairs trap air
  • Heat Response: Vasodilation, sweating

Endocrine System

  • Network of glands releasing hormones
  • Pituitary Gland: Master gland controlling others
  • Adrenal Glands: Secrete adrenaline
  • Pancreas: Secretes insulin and glucagon
  • Ovaries & Testes: Secrete sex hormones
  • Thyroid Gland: Secretes thyroxine

Blood Glucose Control

  • Insulin: Lowers blood glucose by converting it to glycogen in liver
  • Glucagon: Raises blood glucose by breaking down glycogen in liver
  • Maintained by negative feedback cycle

Diabetes

  • Type 1: Lack of insulin – treated with injections
  • Type 2: Insulin resistance – treated with diet, exercise, and medication

Water and Nitrogen Balance

  • Excretion: Removal of excess water, ions, and toxins
  • Osmosis: Maintains cell function and size
  • Urea Production: From breakdown of amino acids (converted to urea in the liver, filtered by kidneys)
  • Kidney Function: Filters blood, reabsorbs useful substances, forms urine

Kidney Treatments

  • Dialysis: Machine filters blood
  • Transplant: Requires tissue match, lifelong immunosuppressants

ADH and Water Control

  • Antidiuretic Hormone (ADH): Regulates urine concentration
  • High Blood Water: Less ADH, more urine
  • Low Blood Water: More ADH, less urine

Reproductive Hormones and Menstrual Cycle

  • Testosterone: Controls sperm production
  • FSH & LH: Control egg maturation and release
  • Estrogen & Progesterone: Build and maintain uterus lining
  • Cycle: 28 days, ovulation around day 14

Menstrual Cycle Hormone Interaction

  • FSH: Stimulates egg maturation, increases estrogen
  • Estrogen: Inhibits FSH, increases LH
  • LH: Triggers ovulation
  • Progesterone: Maintains uterus lining, inhibits FSH and LH

Contraception

  • Hormonal Methods: Pill, patch, implant, IUD
  • Barrier Methods: Condoms (also prevent STIs), spermicide, IUD
  • Sterilization: Permanent solution
  • Evaluation: Efficiency, side effects, and benefits

Infertility Treatments

  • Fertility Drugs: FSH and LH injections
  • IVF: Egg and sperm combined in lab, embryo implanted in uterus
  • Evaluation: Stressful, multiple births, ethical issues

Hormones Overview

  • Thyroxine: Regulates metabolism, controlled by TSH and negative feedback
  • Adrenaline: Fight or flight response, not negative feedback controlled
  • Plant Hormones: Control growth responses to light (phototropism) and gravity (geotropism)

Plant Tropisms

  • Phototropism: Shoots grow towards light
  • Geotropism: Roots grow downwards

Hormone Use in Agriculture

  • Auxins: Weed killers, rooting powders
  • Ethene: Controls fruit ripening
  • Gibberellins: End dormancy, promote flowering and increase fruit size

Reproduction

  • Sexual Reproduction: Fusion of male (sperm) and female (egg) gametes
  • Asexual Reproduction: Single parent, identical offspring
  • Meiosis: Produces gametes with half the chromosome number
  • Fertilization: Combines gametes, restores full chromosome number
  • Mitosis: Growth and repair, identical cells

Comparing Meiosis and Mitosis

  • Meiosis: Two divisions, four non-identical haploid cells
  • Mitosis: One division, two identical diploid cells

Genetics

  • DNA: Polymer of nucleotides, double helix structure, genes code for proteins
  • Genotype and Phenotype: Genotype is genetic makeup, phenotype is observable traits
  • Inheritance: Dominant and recessive alleles
  • Punnett Squares: Predict offspring genotypes and phenotypes
  • Inherited Disorders: Cystic fibrosis (recessive), polydactyly (dominant)
  • Embryo Screening: For genetic conditions, ethical considerations

Use of DNA

  • Human Genome Project: Mapped human genome, helped in disease study and treatment