Human Body Systems
Complete SSC GD Syllabus Coverage
Biology is one of the most important topics in SSC GD. Most questions come from human body organs, systems, functions, diseases, vitamins, digestion, respiration, blood, hormones, etc. This article explains all human body systems in clear, exam-oriented language.
1. Human Body – Basic Overview
The human body is made up of:
Cells → Tissues → Organs → Organ Systems
Total body systems: 11 major systems (as per NCERT)
SSC GD mostly asks from:
- Digestive system
- Respiratory system
- Circulatory system
- Nervous system
- Excretory system
- Skeletal & muscular system
- Endocrine (hormones)
- Reproductive system
2. Digestive System
Function: Converts food into nutrients and energy.
Main Organs and Functions:
- Mouth – chewing and mixing food with saliva
- Esophagus – food pipe
- Stomach – stores food; secretes HCl and pepsin
- Liver – largest gland; produces bile
- Gallbladder – stores bile
- Pancreas – secretes insulin and digestive enzymes
- Small Intestine – main site of digestion
- Large Intestine – absorbs water
- Rectum – stores waste
- Anus – expels waste
Important Points for SSC GD:
- Largest gland → Liver
- Longest organ → Small intestine
- Digestive juice with no enzyme → Bile
- Carbohydrate digestion starts in → Mouth
- Saliva contains enzyme amylase (breaks starch)
- Insulin regulates blood sugar
3. Respiratory System
Function: Exchange of gases (oxygen and carbon dioxide)
Main Organs:
- Nose
- Pharynx
- Larynx
- Trachea
- Bronchi
- Lungs
- Alveoli (functional unit where gaseous exchange occurs)
Breathing Process:
- Inhalation: Oxygen enters lungs
- Exhalation: CO₂ is released
- Hemoglobin in blood carries oxygen
Important SSC Points:
- Respiration occurs in → Mitochondria
- Breathing organ → Lungs
- Functional unit of lungs → Alveoli
- Gas that we inhale maximum → Nitrogen (78% air composition)
4. Circulatory System
Function: Transport of blood, oxygen, nutrients, hormones.
Main Organs:
- Heart – muscular organ with four chambers
- Right atrium
- Right ventricle
- Left atrium
- Left ventricle
Blood Vessels:
- Arteries – carry blood away from heart
- Veins – carry blood toward heart
- Capillaries – smallest blood vessels
Blood Components:
- RBC – carries oxygen (red due to hemoglobin)
- WBC – fight infections
- Platelets – help in clotting
- Plasma – liquid part
Blood Groups:
- A, B, AB, O
- Universal Donor → O negative
- Universal Recipient → AB positive
Important SSC Points:
- Largest artery → Aorta
- Red color of blood → Hemoglobin
- Clotting vitamin → Vitamin K
- Blood formed in → Bone marrow
- Heartbeat: Normal = 72 beats per minute
5. Excretory System
Function: Removal of waste from the body
Main Organs:
- Kidneys – filter blood
- Ureter – carries urine to bladder
- Urinary bladder – stores urine
- Urethra – passes urine out
Kidney Functional Unit:
Nephron
Important SSC Points:
- Functional unit of kidney → Nephron
- Excretory product in humans → Urea
- Study of kidneys → Nephrology
6. Nervous System
Function: Controls body actions, responses, and coordination.
Three Parts:
- Central Nervous System (CNS) - Brain and spinal cord
- Peripheral Nervous System - Nerves
- Autonomic Nervous System - Involuntary actions (heartbeat, digestion)
Brain Parts:
- Cerebrum – largest, intelligence, memory
- Cerebellum – balance and coordination
- Medulla oblongata – involuntary actions (breathing, heartbeat)
Sense Organs:
- Eyes
- Ears
- Nose
- Tongue
- Skin
Important SSC Points:
- Largest part of brain → Cerebrum
- Balance control → Cerebellum
- Memory → Cerebrum
- Spinal cord connects brain to body
7. Skeletal and Muscular System
Skeletal System
Supports body and protects organs.
- Total bones in adult human body: 206
- Largest bone: Femur (thigh bone)
- Smallest bone: Stapes (ear)
Muscular System
Muscles help in movement.
Types of muscles:
- Voluntary (skeletal)
- Involuntary (smooth)
- Cardiac (heart)
8. Endocrine System (Hormones)
Hormones are chemicals released by glands.
Important Glands and Their Hormones:
- Pituitary gland – master gland, controls growth hormone
- Thyroid – secretes thyroxine, controls metabolism
- Pancreas – insulin, controls blood sugar
- Adrenal gland – adrenaline, fight or flight hormone
- Ovary – estrogen, progesterone
- Testes – testosterone
Important SSC Points:
- Master gland → Pituitary
- Diabetes caused by → Lack of insulin
- Goiter caused by → Iodine deficiency
- Thyroid deficiency → Goiter
9. Reproductive System (Basics)
Male:
- Testes – produce sperms and testosterone
Female:
- Ovaries – produce eggs and hormones
- Fertilization occurs in fallopian tube
- Embryo develops in uterus
10. Immune System
Provides protection against diseases.
- White blood cells (WBC)
- Antibodies
- Lymph nodes
- Vaccines help build immunity
11. Important Vitamins and Deficiency Diseases
Vitamin A
For vision
Deficiency: Night blindness
Vitamin B1
Deficiency: Beri-Beri
Vitamin C
For immunity
Deficiency: Scurvy
Vitamin D
For bones
Deficiency: Rickets
Vitamin K
For blood clotting
Deficiency: Excess bleeding
Vitamin B12
For nerves
Deficiency: Anemia
12. Diseases and Their Causes
Bacterial Diseases:
- Tuberculosis
- Cholera
- Typhoid
- Pneumonia
Viral Diseases:
- Common cold
- Measles
- Polio
- Dengue
- COVID-19
Protozoan Diseases:
- Malaria – Plasmodium (mosquito-borne)
Fungal Diseases:
- Ringworm
13. Human Organs and Their Functions (Short Notes)
- Heart – pumps blood
- Brain – controls body
- Kidney – excretes waste
- Liver – detoxification, bile production
- Stomach – digestion
- Skin – largest organ, protection
- Lungs – respiration
- Pancreas – secretes insulin
- Small intestine – absorbs nutrients
14. Quick Revision Table
| System | Major Organs | Key Function |
|---|---|---|
| Digestive | Stomach, liver, intestine | Digestion, absorption |
| Respiratory | Lungs, trachea | Gas exchange |
| Circulatory | Heart, blood | Transport |
| Excretory | Kidney | Waste removal |
| Nervous | Brain, nerves | Coordination |
| Endocrine | Glands | Hormone control |
| Skeletal | Bones | Support |
| Muscular | Muscles | Movement |
15. Memory Tricks for SSC GD
- Largest gland → Liver
- Largest organ → Skin
- Functional unit of kidney → Nephron
- Functional unit of lungs → Alveoli
- Blood clotting → Vitamin K
- Night blindness → Vitamin A deficiency
- Diabetes → Lack of insulin
- Thyroid hormone → Thyroxine
- Universal donor → O negative
- Universal recipient → AB positive
Developed By Satyam kumar
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