Human Body: Anatomy and Physiology

The human body refers to the entire structure of a human being. It is comprised of a variety of cell types that function together to form tissues, organs, and organ systems.

• They maintain homeostasis and the viability of the human body.
• It consists of a head, hair, neck, torso (including the thorax and abdomen), arms and hands, legs, and feet.

The study of the human body is majorly divided into four parts, which are:

• Anatomy: It is the study of the human body, its structure, and parts of the body.
• Physiology: It is the study of physical and chemical functions performed by the cells and organs inside the human body.
• Histology: It entails studying the anatomical structure of cells and tissues.
• Embryology: It is the study of gametes production, embryo development, and congenital disorders.

Key Terms: Human anatomy, Physiology, Histology, Embryology, Skeleton, Muscles, Central nervous system, Human body, Circulatory system, Digestive system

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Human Anatomy

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Human Anatomy is the discipline of biology that studies the human body, structure, and components of the human body. Human Anatomy can be classified into two parts :

• Gross Anatomy: It is the study of body structures that can be viewed without the use of a microscope.
• Microscopic Anatomy: It is the study of microscopic structures that can not be seen with the bare eye and must be studied under a microscope.

Skeleton

The human body functions in a number of ways, including walking, running, crawling, jumping, and climbing.

• The skeleton serves as the structure for all of these actions.
• Humans have up to 300 bones at birth. However, as people become older, their bones begin to fuse.
• At maturity, the total number of bones has decreased to 206. 
• The skeleton also protects many essential organs, including the heart, lungs, and liver.
• Ligaments, which are fibrous connective tissues, connect bones to one another.
• Joints are the locations where two or more bones contact.
• They enable a variety of motions, including rotation, abduction, adduction, protraction, and retraction.
• Joints are classed as moveable or immovable based on their flexibility and movement.
• Movable joints are flexible, but immovable joints (also known as fixed joints) are rigid because the bones are fused.

Muscles

Muscles are special types of tissues that support the movement of the human body. Muscles also help in the movement of internal organs like the contraction of hearts, lungs, etc.

• Muscles help in maintaining body posture and also circulate blood throughout the human body. 
• Although joints aid in bone flexibility, a bone cannot be bent or stretched until a muscle works on it.
• To put it another way, the muscles connected to that bone pull it in the direction of movement.
• Tendons attach the muscles to the bones. The contraction and relaxation of the muscles cause the movement of limbs.

Human Anatomy

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List of Human Body Parts

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The human body consists of a head, a neck, and four limbs that connect to a torso.

• The skeleton, composed of cartilage and bone, gives shape to the body.
• Internal body organs such as the lungs, heart, and brain are enclosed by the skeletal system.
• The spinal cord connects the brain to the rest of the body.

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Human Body Structure

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The human body has many cavities that contain different organ systems.

• The cranial cavity is a space within the skull that protects the brain and other parts of the central nervous system.
• The pleural cavity provides protection for the lungs.
• The abdominal cavity contains the intestines, liver, and spleen.

Humans evolved separately from other animals, but since humans have a distant common ancestor, we mainly have a body layout comparable to other organisms, with the muscles and bones in different proportions.

• For example, we may suppose that giraffes have more vertebrae in their necks than humans.
• No, despite their large height, giraffes have the same number of vertebrae, which includes seven vertebrae in the neck.
• One of our most distinguishing characteristics is our ability to use our hands, particularly for actions that require dexterity, such as writing, opening a bottle of water, and turning a doorknob.
• This results from human ancestors walking on their hind limbs rather than all four.
• The dissection of corpses (cadavers) provided us with the majority of our anatomical information, and it was the only method we could learn about the human body for a long time.
• It was a very disgusting thing, yet it constituted the majority of medical literature for decades.
• Nowadays, innovations in technology have made it feasible to study human anatomy at the microscopic level.

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Human Physiology

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Human Physiology is the study of physical and chemical functions performed by the cells and organs inside the human body.

• It focuses on the body organs, detailed functioning of the human body, and different mechanisms going inside the body. 
• Human Physiology combines health, medicine, and science to explore how the human body adapts to physical exercise, stress, and disease.
• One who studies human physiology is called a physiologist.

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Circulatory System

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The circulatory system is made up of the heart and blood vessels. The human heart is a homologous organ. The circulatory system is a network of arteries, veins, and capillaries, that are all linked by the heart to provide oxygen and nutrients to various areas of the body.

• It also carries away wastes from different body parts.
• The circulatory system also maintains the temperature of the body, thus regulating homeostasis. 
• The circulatory system is also called the cardiovascular system.
• It is known as the transport system of the body because blood flows through the body and carries oxygen, nutrients, and waste through the body.

The different types of circulation in the human body are

• Systemic circulation: It supplies the functioning blood that transports oxygen and nutrients to all tissues throughout the body.
• Pulmonary circulation: It transports the deoxygenated blood from the ventricles and gives back the oxygenated blood.
• Coronary circulation: It circulates the blood through the heart. The oxygenated blood is supplied to the heart muscles and takes away the deoxygenated blood from them.

Circulatory system

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Digestive System

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The digestive system is responsible for breaking down food, absorbing nutrients, and transmitting the nutrients to the body. These nutrients help in the development of the body and cell repair.

The digestive system consists of many body parts, which are:

• Mouth
• Tongue
• Teeth
• Oesophagus
• Stomach
• Pancreas
• Liver
• Gastrointestinal tract
• Small intestines
• Large intestines
• Rectum

The process of digestion is explained here:

• Digestion starts as soon as we eat food. The process of digestion starts from the mouth by chewing the food.
• The food breaks into smaller parts and mixes with saliva to form a small mass, known as a bolus. The bolus can be swallowed easily.
• From the mouth, the food passes through the esophagus and reaches the stomach.
• Enzymes and acids are secreted by the stomach, which breaks the food into a paste.
• The food then travels into the small intestine.
• The food is further broken down by bile released by the liver and strong digestive enzymes secreted by the pancreas.
• All the nutrients present in the food are absorbed.
• After the absorption of nutrients, the leftover food or the waste is sent to the large intestine.
• The water is removed from the waste and then it is pushed to the rectum.
• The waste can then be removed from the body in the form of stool.

Digestive system

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Respiratory System

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The respiratory system provides oxygen to the body and takes out the carbon dioxide from the body.

• The lungs are the main organ of the respiratory system.
• The respiratory system is also called the ventilatory system, respiratory apparatus, or gas exchange system.

The respiratory system consists of many body organs, which are:

• Lungs
• Trachea
• Diaphragm
• Bronchi
• Bronchioles

While breathing the air passes through the nose to the sinuses, which serve to control the temperature of the air. The inhaled air then passes down the windpipe, commonly known as the trachea.

• After the trachea, the air flows into the bronchial passages.
• The bronchial tubes contain a cilia lining, which holds mucous.
• Mucous is a sticky fluid that acts as the initial barrier, trapping dust and other tiny foreign particles in the air we breathe.
• The air reaches the lungs, the respiratory system works along with the circulatory systems to convert deoxygenated blood into oxygenated blood and circulate oxygenated blood throughout the body.
• The respiratory system then throws out the carbon dioxide from the body via the nose.

Respiratory system

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Nervous System

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The nervous system is a complicated network of nerves that transmits signals from the brain to other body parts.

• These signals (also called impulses) are coded messages that inform the brain about what is going on, and the brain responds by sending impulses that are reactions to the stimuli.
• The nervous system consists of nerve cells, the brain, the spinal cord, and fibers that convey nerve signals to and from the various body parts.

The nervous system can be divided into two types:

• Central nervous system
• Peripheral nervous system

Central Nervous System

The central nervous system is made up of the brain and the spinal cord. It maintains all the voluntary actions ( like taking, walking, eating, etc) and involuntary actions (like blinking, breathing, sneezing, etc) of the human body. 

• It receives the signal from all the body parts and sends back the signal in response to it.
• These signals are carried by the spinal cord. The central nervous system controls the mind, body parts, functions, and movements.

The central Nervous system is divided into three parts:

Forebrain

It is the largest part of the brain, responsible for regulating motor function, thinking, receiving, and processing information from the body parts. The forebrain is made up of three parts, namely the cerebrum, hypothalamus, and thalamus.

Midbrain

The midbrain is the central area of the brainstem and it is comparatively smaller in size. It is located between the hypothalamus and the thalamus. The midbrain is mainly made of two parts which are called the Tectum, and Tegmentum.

Hindbrain

The hindbrain is the central part of the brain. It regulates all the body functions required for survival like breathing, sleep, heart beating, motor learning, and consciousness. The Hindbrain is made of three parts which are called Cerebellum, Medulla, and Pons.

Peripheral Nervous System

The Peripheral nervous system is made up of the nerves and ganglia which are located outside the brain and spinal cord. It functions independently of the brain and spinal cord. 

• The nerves of the peripheral nervous system are linked to the sensory organs and also connect the Central Nervous system to the rest of the body.
• The nerves of the Peripheral Nervous System are referred to as Axons.

The Peripheral Nervous System is divided into two parts:

Somatic Nervous System

The Somatic Nervous System transfers the motor and sensory impulses to and from the central nervous system. It is connected to the skeletal system, limbs, and sensory organs and controls the voluntary motion of the body.

Autonomic Nervous System

The Autonomic Nervous System transmits signals from the central nervous system to involuntary organs and smooth muscles to protect against abnormal conditions and attacks. It controls the involuntary motions of the body.

Nervous System

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Reproductive System

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The human reproductive system consists of both internal and external organs. These reproductive organs are responsible for producing offspring or children.

• Hormones, fluids, and pheromones help the reproductive organs to operate properly.
• The process of reproduction entails the mixing of genetic information and the production of gametes.
• The reproductive system differs in the male and female bodies.

Male Reproductive System

The male reproductive system has a penis, testes, scrotum, Vas deferens, epididymis, and seminal vesicles. and the Prostate glands. 

• The sperm are produced and stored in the testes, which are protected by the scrotum.
• Vas deferens is located near the scrotum.
• To keep the testes lubricated and protected, sperms are combined with fluids from numerous glands, including the seminal glands, prostate gland, and Cowper’s gland.
• The Cowper’s gland increases the sebum volume and lubrication during coitus.

Male Reproductive System

Female Reproductive System

The Female Reproductive System has the vagina, cervix, ovaries, uterus, endometrium, and Uterine tubes. The female body has a pair of ovaries that generate eggs and the female hormone estrogen. 

• The cervix is the pathway to the vagina and the entry point for sperm.
• The vaginal canal serves as the route for the penis during intercourse and the exit point for the fetus during birth.
• The Uterus tubes or the fallopian tubes connect the uterus to the ovaries and transport eggs to the uterus for fertilization.
• When the sperm fertilizes with the egg, a gamete is formed which later turns into an embryo.
• The fertilization takes place in the uterus, also called the womb. The embryo is nurtured inside the uterus until birth.

Female Reproductive System

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Urinary System

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The urinary system is made up of two kidneys, renal arteries, Nephrons, Ureter, and Urethra.

• The kidneys are linked to the bladder via ureters and open into the urethra.
• The urinary system excretes waste from the body as urine.
• It also monitors blood pressure, controls metabolite and electrolyte levels, and maintains blood pH.
• The kidney filters out the blood and removes the waste present in the blood. The renal arteries carry blood to the kidney. 
• Nephrons are responsible for blood purification and the subsequent production of urine, which ultimately exits the kidneys via the renal veins and is removed from the body in the form of urine.
• A healthy person generates 800-2000 ml of urine every day.

Urinary System

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Things to Remember

• The human body is comprised of a variety of cell types that function together to form tissues, organs, and organ systems.
• Anatomy is the study of the human body, its structure, and parts of the body.
• Humans have up to 300 bones at birth.
• Muscles are special types of tissues that support the movement of the human body.
• The human body consists of a head, a neck, and four limbs that connect to a torso.
• Human Physiology is the study of physical and chemical functions performed by the cells and organs inside the human body.
• The circulatory system is made up of the heart and blood vessels.
• The digestive system is responsible for breaking down food, absorbing nutrients, and transmitting the nutrients to the body.