The Human Body - Reproduction, Excretion, and Respiratory Systems

What is Reproduction?

- Reproduction is the process of giving rise to young ones (offspring) of the same kind.
- The Male reproductive cell is known as a sperm (plural: sperms). It is produced in the testes.
- A female reproductive cell is known as an ovum (plural: ova). It is produced in the ovaries.
 

Fertilization in Humans

- Fertilization is the union of a sperm cell and an ovum
- During sexual intercourse, the penis (male organ) deposits sperms in the vagina (female organ)
- The sperms swim up to the fallopian tube (oviduct) via the uterus where they get to the ovum.
- Fusion process (where the sperm enters the ovum forming a zygote.

Development of the Foetus

- After fertilization, the sperm and the ovum form a single cell called a zygote.
- The zygote undergoes cell division changing into a cell called an embryo.
- The embryo (which is a growing cell) moves down to the uterus (womb) developing fingerlike structures called placenta.
- The embryo attaches itself to the uterine wall in a process called implantation.
- The embryo then grows to become a foetus
 

Functions of the Placenta

- Facilitates production of necessary hormones to maintain the pregnancy
- Enhances exchanges of oxygen from the mother's body to the foetus
- Enhances the exchange of carbon dioxide from the foetus to the mother's body
- Prevents disease-causing germs from reaching the foetus.

Functions of the umbilical cord

- Joins the placenta to the foetus
- It passes oxygen and nutrients from the placenta to the foetus' bloodstream
- It passes carbon dioxide and nitrogenous wastes from the foetus to the placenta.

Amniotic fluid

- It is found within the amnion sac of the mother. - Functions of the amniotic fluid
- Cushions the foetus from shock
- Allows easier foetal movement
- Controls the temperature to allow for safe growth of the foetus
- Lubricates the foetus
- Prevents dehydration by providing moisture.

The process of birth

(In humans the birth process occurs during the gestation period, usually 9 months)

1. The uterine wall contracts - also known as labour
2. Following the contraction of the uterine wall, the amnion breaks, releasing fluids. The head of the foetus is pushed down the cervix
3. Cervix enlarges (dilates) allowing the passage of the foetus down to the vagina
4. The enlarged vagina allows the foetus, to come out, head first
5. When the baby is out, the umbilical cord is tied and cut to separate the baby from the mother
6. During afterbirth - part of the umbilical cord and placenta comes out

What is Excretion?

Excretion is the removal of waste products from the body
In humans, the major waste products are urea, carbon dioxide, excess water, and excess salts
The organs responsible for the removal of waste are:

• Skin - Removes excess water and salts in the form of sweat
• Lungs - Removes carbon dioxide and water vapour through exhalation
• Kidneys - Removes urea and excess water in the form of urine

The Skin

Below is a picture of the skin, as an excretory system

The Kidney

Below is a labelled diagram of the kidney, as an excretory system

Functions of parts of the Kidney

1. Renal Capsule is a thin and tough outer membrane that surrounds the kidney.
2. Renal Pelvis is connected to the upper part of the ureter. It collects urine from the nephrons and directs it to the ureter.
3. Medulla is the innermost part of the kidney. It is formed up of renal pyramids.
4. Cortex is the outer region of the kidney. It is formed up of nephrons that are used in the filtration of the blood.
5. Nephrons are the functional units of the kidneys. They play the fundamental function of filtration of the blood.
6. Ureter collects filtrate (urine) from the renal pelvis and takes it to the bladder.
7. Renal Artery branches off the aorta and brings unfiltered blood into the kidney for filtration.
8. Renal Vein takes filtered blood from the kidney into the inferior vena cover.

Kidney Filtration Process

There are three major steps in the filtration of the blood in the kidney. Once the blood enters the kidneys, three processes occur:

1. The unfiltered blood enters the nephrons where filtrate is made. This process is known as glomerular filtration. Blood is filtered through capillaries in the nephrons identified as glomeruli.
2. The tubules in the nephrons reabsorb the filtered blood back into the capillaries, which then makes its way into the renal vein. This process is known as tubular reabsorption.
3. The filtrate(waste) collected in the glomerular filtration process passes through tubules which then makes its way into the renal pelvis and into the ureter. This process is known as tubular secretion.

What is the respiratory system?

The respiratory system consists of different organs that help remove carbon dioxide (a waste gas) from the body and put oxygen into the blood.
Below is a labelled diagram of the respiratory system.

Functions of Major Parts of the Respiratory System

1. Diaphragm is a sheet of muscle that helps pull in oxygen-rich air and push out carbon dioxide-rich air from the lungs.
2. Ribs are bones that form a cage that protects the lungs and heart and other critical organs of the body.
3. Mouth and Nose help pull air from the environment into a body's respiratory system
4. Sinuses help regulate the temperature and humidity of the air breathed in.
5. Pharynx connects to the trachea for air delivery.
6. Trachea connects the lungs and the throat.
7. Bronchus (Bronchial Tubes) is located at the bottom of the trachea and branches off to each of the lungs.
8. Right and Left Lungs are responsible for removing carbon dioxide from the blood and putting oxygen into the blood.
9. Bronchioles smaller branches of the bronchus(bronchial Tubes) that connect to the alveoli in the lungs.
10. Alveoli are tiny air sacs in the lungs where the exchange of carbon dioxide and oxygen from and to the blood respectively takes place.
11. Capillaries are blood vessels and are part of the human circulatory system. Within the respiratory system, capillaries are found on the alveoli walls, where carbon dioxide is removed from the blood and oxygen is put into the blood.