Human physiology is the study of how different organs and organ systems of the human body work.
The human body performs many life processes such as digestion, respiration, circulation, excretion, coordination, movement and growth. These processes are carried out by different systems that work together in a coordinated manner.
Table of Contents
Part 1: Digestive System
What Is Digestion?
Digestion is the process by which complex food is converted into simple absorbable substances.
It includes both:
- Mechanical processes
- Chemical processes
Main Steps Of Digestion
The main steps in digestion are:
Ingestion → Digestion → Absorption → Assimilation → Egestion
| Step | Meaning |
|---|---|
| Ingestion | Taking food into the body |
| Digestion | Breaking food into simpler substances |
| Absorption | Taking digested food into the blood |
| Assimilation | Conversion of absorbed food into body material |
| Egestion | Removal of undigested waste |
Components Of Digestive System
The digestive system has two main parts:
- Alimentary canal
- Digestive glands
Mouth And Buccal Cavity
The mouth is the space where food is chewed and mixed with saliva.
The mouth opens into the buccal cavity, which contains:
- Teeth
- Tongue
- Salivary glands
Tongue
The tongue is a fleshy muscular organ attached to the floor of the buccal cavity.
Functions Of Tongue
- Helps in chewing
- Helps in swallowing
- Helps in tasting food
- Helps in speech
Saliva And Salivary Glands
Saliva is secreted by salivary glands.
The first enzyme to mix with food in the digestive tract is amylase.
Amylase helps in the digestion of starch.
Pancreas
The pancreas plays an important role in digestion.
It secretes:
- Lipase
- Amylase
- Protease
These enzymes help in the digestion of fats, carbohydrates and proteins.
Part 2: Excretory System
What Is Excretion?
Excretion is the process of elimination of metabolic wastes from the body.
What Is Osmoregulation?
Osmoregulation is the process of removing excess water from the body or maintaining constant water content.
Types Of Nitrogenous Excretion
Ammonotelism
Ammonotelism is the elimination of nitrogen mainly in the form of ammonia.
Examples:
- Aquatic invertebrates
- Bony fishes
- Amphibians
Ureotelism
Ureotelism is the elimination of nitrogen mainly in the form of urea.
Ammonia combines with carbon dioxide in the liver to form urea.
Examples:
- Mammals
- Humans
- Frogs
- Toads
Uricotelism
Uricotelism is the elimination of nitrogen mainly in the form of uric acid.
Examples:
- Birds
- Reptiles
- Many insects
Excretory Organs In Invertebrates
| Organism | Excretory Organ |
|---|---|
| Tapeworm | Flame cells |
| Sponges | Water canal system |
| Hydra | Coelenteron |
| Annelids | Nephridia |
| Insects | Malpighian tubules |
| Prawns | Green glands |
| Amoeba | Plasmalemma |
| Spiders | Coxal glands |
Human Excretory System
The human excretory system includes:
- Kidney
- Ureters
- Urinary bladder
- Urethra
Kidney
The kidney is a paired, bean-shaped organ present in the abdomen below the diaphragm.
The left kidney is slightly higher than the right kidney.
Functions Of Kidney
- Forms urine
- Removes nitrogenous waste
- Maintains water balance
- Helps in osmoregulation
Water reabsorption in the kidney is controlled by ADH, or Antidiuretic Hormone.
Nephron
The nephron is the functional unit of the kidney.
Each kidney has around 1 million nephrons.
Parts Of Nephron
The nephron has two main parts:
- Bowman’s capsule
- Renal tubule
Bowman’s Capsule
Bowman’s capsule contains a network of blood capillaries called the glomerulus.
Together, Bowman’s capsule and glomerulus form the Malpighian body.
Blood enters the glomerulus through the afferent arteriole and leaves through the efferent arteriole.
Path Of Urine Flow
The correct path of urine flow is:
Kidney → Ureter → Urinary Bladder → Urethra
Part 3: Nervous System
What Is Nervous System?
The nervous system is a control system of the body.
It works with the endocrine system to coordinate different body parts and maintain body functions.
It gives the ability to:
- Think
- Understand
- Receive stimuli
- Give responses
Neuron
The neuron is the structural and functional unit of the nervous system.
Structure Of Neuron
A neuron has three main parts:
- Cell body
- Dendrites
- Axon
Cell Body
The cell body is also called cyton.
It contains:
- Nucleus
- Cytoplasm
- Cell organelles
- Nissl’s granules
Dendrites
Dendrites conduct nerve impulses towards the cell body.
They are called afferent processes.
Axon
The axon conducts nerve impulses away from the cell body.
It is a long, thick and cylindrical structure covered with Schwann cells.
If the axon is covered by a myelin sheath, it is called myelinated.
If myelin sheath is absent, it is called non-myelinated.
Nodes Of Ranvier
Nodes of Ranvier are the places on the axon where the myelin sheath is absent.
Functions Of Neuron
- Receives stimuli from the environment
- Sends responses
- Regulates biological activities
- Helps in coordination
Synapse
A synapse is the gap between two neurons.
It helps in the transmission of nerve impulses from one neuron to another.
Brain And Spinal Cord
The central nervous system includes:
- Brain
- Spinal cord
Pons
The pons is a swelling between the medulla and midbrain.
It acts as a bridge between different parts of the brain and helps regulate breathing.
Hindbrain
The hindbrain controls activities such as:
- Muscular activities
- Breathing
- Coughing
Cerebellum
The cerebellum is the second largest part of the brain.
It helps in body balance and coordination of muscular activities.
Spinal Cord
The spinal cord extends from the base of the brain up to the second lumbar vertebra.
In adults, it is around 42 to 45 cm long.
Functions Of Spinal Cord
- Carries stimuli to and from the brain
- Acts as the centre of spinal reflex action
Peripheral Nervous System
The peripheral nervous system includes nerves that arise from the central nervous system and connect with receptor and effector organs.
Part 4: Endocrine System
What Is Endocrine System?
The endocrine system is a system of glands that secrete hormones directly into blood or lymph.
These hormones control:
- Body functions
- Metabolism
- Growth
- Stress response
Endocrinology
Endocrinology is the branch of biology that studies endocrine glands, hormones and their effects.
Thomas Addison is known as the Father of Endocrinology.
Hormones
Hormones are active organic messenger compounds secreted by endocrine glands.
They circulate through blood and affect different body organs.
The term hormone was coined by E.H. Starling.
In 1903, Bayliss and Starling extracted the first hormone from the duodenal mucosa and named it secretin.
Types Of Hormones
| Type | Examples |
|---|---|
| Protein hormones | Pituitary, parathyroid, hypothalamus and pancreatic hormones |
| Steroid hormones | Adrenal cortex and gonadal hormones |
| Amino acid derivatives | Thyroid hormones and adrenal medulla hormones |
Pituitary Gland
The pituitary gland is a pea-shaped endocrine gland present at the base of the midbrain below the hypothalamus.
It is also called the master gland because it controls many other endocrine glands.
Parts Of Pituitary Gland
- Adenohypophysis
- Neurohypophysis
Important Endocrine Fact
The pituitary gland is not found in pairs.
Adrenal glands, testes and ovaries are paired glands, but the pituitary gland is single.
Part 5: Locomotory System
What Is Locomotory System?
The locomotory system helps the human body in movement and locomotion.
It works with:
- Skeletal system
- Muscular system
- Joints
Skeletal System
The skeletal system forms the framework of the body.
The study of bones is called osteology.
Number Of Bones In Human Body
| Stage | Number Of Bones |
|---|---|
| Adult human | 206 bones |
| Newborn baby | About 300 bones |
Many bones in newborns fuse during growth.
Functions Of Skeletal System
- Provides shape and support
- Protects vital organs like brain, heart and lungs
- Helps in movement
- Produces blood cells through hematopoiesis
- Stores minerals like calcium and phosphorus
Division Of Human Skeleton
The human skeleton is divided into:
- Axial skeleton
- Appendicular skeleton
Axial Skeleton
The axial skeleton forms the central axis of the body.
It contains 80 bones.
It includes:
- Skull
- Vertebral column
- Ribs
- Sternum
Key Takeaways
- Human physiology explains how the human body works.
- The digestive system breaks food into absorbable substances.
- The excretory system removes metabolic waste and maintains water balance.
- The nervous system controls quick responses and coordination.
- The endocrine system controls body functions through hormones.
- The locomotory system helps in movement, support and protection.
- Nephron is the functional unit of the kidney.
- Neuron is the functional unit of the nervous system.
- Pituitary gland is known as the master gland.
- The skeletal system protects vital organs and provides body shape.
FAQs On Human Physiology
What is human physiology?
Human physiology is the study of the functions of different organs and organ systems of the human body.
What is digestion?
Digestion is the process of converting complex food into simple absorbable substances.
What are the main steps of digestion?
The main steps are ingestion, digestion, absorption, assimilation and egestion.
Which enzyme first mixes with food?
Amylase is the first enzyme to mix with food in the digestive tract.
What is excretion?
Excretion is the removal of metabolic wastes from the body.
What is the functional unit of kidney?
The nephron is the functional unit of the kidney.
What is the correct path of urine flow?
The correct path is kidney, ureter, urinary bladder and urethra.
What is the functional unit of the nervous system?
The neuron is the structural and functional unit of the nervous system.
What is synapse?
Synapse is the gap between two neurons.
Which part of the brain regulates breathing?
The pons helps in regulating breathing.
What is endocrinology?
Endocrinology is the study of endocrine glands, hormones and their effects.
Who is called the Father of Endocrinology?
Thomas Addison is called the Father of Endocrinology.
Who coined the term hormone?
E.H. Starling coined the term hormone.
Which gland is called the master gland?
The pituitary gland is called the master gland.
What is osteology?
Osteology is the branch of biology that deals with the study of bones.
How many bones are present in an adult human body?
An adult human body has 206 bones.
Last Moment Exam Cheat Sheet – Human Physiology
- Digestion converts complex food into simple absorbable substances.
- The steps of digestion are ingestion, digestion, absorption, assimilation and egestion.
- Amylase is the first enzyme to mix with food in the digestive tract.
- Pancreas secretes lipase, amylase and protease.
- Excretion removes metabolic wastes from the body.
- Humans are ureotelic because they mainly excrete urea.
- Kidney, ureter, urinary bladder and urethra form the human excretory system.
- Nephron is the functional unit of the kidney.
- Bowman’s capsule is responsible for filtration of blood.
- Neuron is the structural and functional unit of the nervous system.
- Synapse is the gap between two neurons.
- Pons helps in regulating breathing.
- Spinal cord is the centre of spinal reflex action.
- Endocrine glands release hormones directly into blood or lymph.
- Thomas Addison is known as the Father of Endocrinology.
- E.H. Starling coined the term hormone.
- Secretin was the first hormone extracted by Bayliss and Starling.
- Pituitary gland is called the master gland.
- Osteology is the study of bones.
- Adult humans have 206 bones.
- Newborn babies have about 300 bones.