Section I – Animal Physiology

1. Nutritive Substances, Enzymes and Energetics

1.1 Biological Role of Nutritive Substances

Nutritive substances are chemical substances required by organisms for energy production, growth, development, repair of tissues, maintenance of cellular structures and regulation of physiological processes.

The major nutrients include carbohydrates, proteins, lipids, vitamins, minerals and water. Each nutrient has a particular physiological role, although their functions are closely interconnected.

1.2 Carbohydrates

Carbohydrates are organic compounds mainly composed of carbon, hydrogen and oxygen. They are important sources of energy for many animals.

Major functions

• Provide energy for cellular activities.
• Glucose serves as an important metabolic fuel.
• Glycogen acts as a storage carbohydrate in animals.
• Carbohydrate intermediates participate in other metabolic pathways.

For example, glucose can be metabolized through glycolysis to produce pyruvate and usable cellular energy.

1.3 Proteins

Proteins are polymers of amino acids linked by peptide bonds. They are essential structural and functional components of cells.

Functions of proteins

• Growth and repair of tissues.
• Formation of enzymes.
• Formation of hormones and receptors.
• Transport of substances.
• Immune defense through antibodies.
• Muscle contraction.

1.4 Lipids

Lipids are hydrophobic or amphipathic organic compounds that include fats, oils, phospholipids and steroids.

Lipids are important because they provide concentrated energy, form biological membranes, protect organs and participate in hormone synthesis.

1.5 Vitamins

Vitamins are organic micronutrients required in small quantities for normal physiological functions.

They generally do not provide energy directly, but many vitamins participate in enzyme systems, metabolism, antioxidant protection, vision, blood formation and maintenance of tissues.

1.6 Minerals

Minerals are inorganic elements required for structural, regulatory and metabolic functions.

1.7 Water

Water is the major component of living organisms and provides the medium in which most biochemical reactions occur.

It also participates in transport, temperature regulation, digestion, excretion and maintenance of cell volume.

1.8 Metabolism

Metabolism refers to the complete set of chemical reactions occurring within a living organism.

Metabolic reactions can be broadly divided into catabolism and anabolism.

1.9 Glycolysis

Glycolysis is a metabolic pathway in which one molecule of glucose is converted into two molecules of pyruvate. It occurs in the cytoplasm and does not directly require molecular oxygen.

Major steps

1. Glucose is phosphorylated.
2. The six-carbon molecule is rearranged.
3. The molecule is split into two three-carbon molecules.
4. The three-carbon molecules undergo oxidation.
5. ATP is produced by substrate-level phosphorylation.
6. Pyruvate is formed.

1.10 Bioenergetics

Bioenergetics is the study of energy transformations in living organisms.

Cells continuously require energy for active transport, biosynthesis, movement, growth, maintenance of membrane gradients and many other functions.

1.11 ATP

Adenosine triphosphate or ATP is the major immediate energy-transfer molecule of cells.

Energy released during nutrient oxidation can be captured in ATP and subsequently used for cellular work.

1.12 Enzymes

Enzymes are biological catalysts that increase the rate of biochemical reactions by lowering the activation energy required for the reaction.

Enzymes are generally highly specific because their active sites possess structural and chemical characteristics that allow particular substrates to bind.

1.13 Mechanism of Enzyme Action

1. The substrate approaches the enzyme.
2. The substrate binds to the active site.
3. An enzyme–substrate complex is formed.
4. The enzyme facilitates the reaction by lowering activation energy.
5. Products are formed.
6. Products leave the active site.
7. The enzyme becomes available for another reaction.

1.14 Factors Affecting Enzyme Activity

• Temperature.
• pH.
• Substrate concentration.
• Enzyme concentration.
• Inhibitors.
• Activators.
• Cofactors.

1.15 Cofactors and Coenzymes

Some enzymes require non-protein components for catalytic activity. These components are called cofactors.

Metal ions such as zinc, magnesium and iron can function as cofactors. Organic cofactors are commonly called coenzymes.

Examples of coenzymes include NAD⁺, FAD and coenzyme A.

2. Digestion

2.1 Introduction

Digestion is the mechanical and chemical breakdown of complex food substances into simpler molecules that can be absorbed and utilized by the body.

The digestive system includes the alimentary canal and associated digestive glands.

2.2 Major Parts of the Alimentary Canal

The alimentary canal extends from the mouth to the anus.

2.3 Saliva

Saliva is secreted by salivary glands and helps in lubrication, formation of the food bolus and initiation of carbohydrate digestion.

Salivary amylase begins the digestion of starch into smaller carbohydrate products.

2.4 Gastric Juice

Gastric juice contains hydrochloric acid, pepsinogen, mucus and other substances.

Hydrochloric acid creates an acidic environment that supports pepsin activity and helps denature proteins.

2.5 Digestion of Proteins

1. Protein enters the stomach.
2. Hydrochloric acid denatures proteins.
3. Pepsinogen is activated to pepsin.
4. Pepsin breaks proteins into smaller peptides.
5. Pancreatic proteases continue digestion in the small intestine.
6. Peptidases produce absorbable amino acids and small peptides.

2.6 Digestion of Carbohydrates

Carbohydrate digestion begins in the mouth and continues mainly in the small intestine.

Pancreatic amylase and intestinal brush-border enzymes convert complex carbohydrates into monosaccharides.

2.7 Digestion of Lipids

Lipid digestion occurs mainly in the small intestine. Bile salts emulsify fats and increase the surface area available for pancreatic lipase.

Products of lipid digestion form micelles and reach the intestinal epithelial surface. Lipid products are then absorbed and reassembled inside enterocytes.

2.8 Absorption

Absorption is the movement of digested nutrients from the gastrointestinal tract into blood or lymph.

3. Respiration

3.1 Introduction

Respiration is the physiological process through which organisms obtain oxygen and eliminate carbon dioxide while supporting cellular energy production.

3.2 Mechanism of Inspiration

1. Inspiratory muscles contract.
2. Thoracic volume increases.
3. Intrapulmonary pressure decreases.
4. Atmospheric air enters the respiratory tract.

3.3 Mechanism of Expiration

1. Inspiratory muscles relax.
2. Elastic recoil reduces thoracic volume.
3. Intrapulmonary pressure increases.
4. Air flows out of the lungs.

3.4 Respiratory Pigments

Respiratory pigments increase the oxygen-carrying capacity of blood or other respiratory fluids.

Haemoglobin is the major respiratory pigment in vertebrate blood.

3.5 Oxygen Transport

Most oxygen is transported reversibly bound to haemoglobin as oxyhaemoglobin, while a smaller fraction is physically dissolved in plasma.

3.6 Carbon Dioxide Transport

Carbon dioxide is transported in dissolved form, bound to proteins and mainly as bicarbonate ions.

3.7 Regulation of Respiration

Respiratory activity is regulated by neural centers and chemical feedback involving carbon dioxide, hydrogen ions and oxygen.

4. Circulation

4.1 Blood Groups

Blood groups are determined by specific antigens present on the surface of red blood cells and antibodies present in plasma.

4.2 Haemostasis

Haemostasis is the physiological process that prevents excessive blood loss after vascular injury.

1. Vasoconstriction.
2. Platelet adhesion.
3. Platelet activation.
4. Platelet aggregation.
5. Coagulation.
6. Formation of a stable fibrin clot.

4.3 Conduction System of Heart

4.4 Cardiac Output

Cardiac output is the volume of blood pumped by one ventricle per minute.

The basic relationship is:

Cardiac Output = Heart Rate × Stroke Volume

5. Excretion

5.1 Introduction

Excretion is the process by which metabolic waste products are removed from the body.

5.2 Nitrogenous Excretory Products

5.3 Nephron

The nephron is the functional unit of the kidney.

It includes the renal corpuscle and renal tubule.

5.4 Urine Formation

1. Glomerular filtration.
2. Tubular reabsorption.
3. Tubular secretion.
4. Concentration and final modification of tubular fluid.

5.5 Kidney and Electrolyte Balance

The kidneys regulate sodium, potassium, calcium, phosphate and water balance by adjusting tubular reabsorption and secretion.

5.6 Kidney and Acid–Base Balance

The kidneys contribute to acid–base homeostasis by secreting hydrogen ions, reabsorbing filtered bicarbonate and generating new bicarbonate.

6. Nervous System

6.1 Neuron

A neuron is a specialized cell responsible for receiving, processing and transmitting information.

6.2 Major Parts of a Neuron

• Cell body.
• Dendrites.
• Axon.
• Axon terminals.

6.3 Electrical Signaling

Neurons maintain an electrical difference across their plasma membranes. Changes in membrane permeability to ions produce electrical signals.

6.4 Action Potential

1. Resting membrane potential.
2. Depolarization.
3. Repolarization.
4. Hyperpolarization.
5. Return toward resting conditions.

6.5 Synaptic Transmission

1. Action potential reaches presynaptic terminal.
2. Calcium channels open.
3. Calcium enters the terminal.
4. Synaptic vesicles release neurotransmitter.
5. Neurotransmitter crosses the synaptic cleft.
6. Neurotransmitter binds to postsynaptic receptors.
7. Postsynaptic response is produced.

6.6 Neuronal Integration

Neuronal integration is the process by which the nervous system combines multiple excitatory and inhibitory inputs to produce an appropriate response.

7. Endocrine System

7.1 Introduction

The endocrine system consists of glands and tissues that release hormones into the internal environment.

7.2 Major Endocrine Glands

7.3 Hormones

Hormones are chemical messengers produced by endocrine cells and carried to target cells where they produce specific physiological effects.

7.4 Peptide Hormone Mechanism

1. Hormone binds to a membrane receptor.
2. Intracellular signaling pathway is activated.
3. Second messengers may be generated.
4. Protein kinases or other effectors are activated.
5. Cellular response occurs.

7.5 Steroid Hormone Mechanism

1. Steroid hormone crosses the plasma membrane.
2. Hormone binds to an intracellular receptor.
3. Hormone–receptor complex interacts with DNA-associated regulatory regions.
4. Gene transcription changes.
5. New proteins are synthesized.
6. Physiological response develops.

7.6 Negative Feedback

Negative feedback is one of the major mechanisms by which endocrine systems maintain physiological variables within appropriate ranges.

8. Sensory System

8.1 General Principles

Sensory receptors detect specific stimuli and convert them into electrical signals that can be processed by the nervous system.

8.2 Vision

The eye is the primary organ of vision. Light is focused onto the retina, where photoreceptors convert light energy into neural signals.

Photoreceptors

• Rods are important for low-light vision.
• Cones are important for color and high-acuity vision.

8.3 Hearing

Sound waves are converted into mechanical vibrations and eventually into neural signals by specialized receptor cells in the inner ear.

8.4 Balance

The vestibular apparatus detects head movement and contributes to maintenance of posture and equilibrium.

8.5 Taste

Taste receptor cells detect dissolved chemical substances and contribute to the perception of taste.

8.6 Smell

Olfactory receptor neurons detect airborne chemical molecules and transmit information to the brain.

8.7 Touch

Cutaneous receptors detect mechanical pressure, vibration, temperature and potentially damaging stimuli.

9. Reproduction and Development

9.1 Female Reproductive Cycle

The female reproductive cycle involves coordinated changes in the ovaries, uterus and reproductive hormones.

9.2 Ovarian Cycle

The ovarian cycle can be divided into follicular, ovulatory and luteal phases.

9.3 Uterine Cycle

The uterine cycle includes menstrual, proliferative and secretory phases.

9.4 Gametogenesis

Gametogenesis is the process of formation and maturation of gametes.

Spermatogenesis

Spermatogenesis is the formation of spermatozoa from spermatogenic cells through mitotic proliferation, meiosis and differentiation.

Oogenesis

Oogenesis is the process by which female gametes develop. It involves growth of oocytes and meiotic divisions.

9.5 Types of Eggs

Eggs may be classified according to the amount and distribution of yolk.

9.6 Fertilization

Fertilization is the process by which male and female gametes interact and their genetic material is combined to establish a zygote.

Major events

1. Sperm reaches the oocyte.
2. Recognition and interaction occur.
3. Acrosomal reactions facilitate penetration.
4. Sperm and oocyte membranes interact.
5. Mechanisms preventing polyspermy become activated.
6. Male and female genetic material combine.
7. Zygote formation occurs.

9.7 Embryonic Development

Early embryonic development includes cleavage, formation of the blastula, gastrulation and subsequent differentiation and organ formation.

🎯 Section I – Final Examination Revision

10-Mark Preparation

• Explain biological roles of nutrients and metabolism.
• Explain enzyme mechanism and factors affecting enzyme activity.
• Describe digestion and absorption of nutrients.
• Explain respiratory mechanism and gas transport.
• Describe blood coagulation and haemostasis.
• Explain the conduction system of the heart.
• Describe urine formation.
• Explain action potential and synaptic transmission.
• Describe major endocrine glands and hormone functions.
• Explain sensory physiology.
• Describe gametogenesis, fertilization and embryonic development.

5-Mark Preparation

2-Mark Rapid Revision

• Define metabolism.
• Define enzyme.
• What is ATP?
• What is glycolysis?
• What is digestion?
• Define respiratory pigment.
• What is cardiac output?
• Define haemostasis.
• What is a nephron?
• Define action potential.
• What is a synapse?
• Define hormone.
• What is a sensory receptor?
• Define gametogenesis.
• What is fertilization?