Digestive System Overview

Digestive System

Salivary Glands:
- There are four main types of salivary glands: parotid, submandibular, sublingual, and Von Ebner glands.
- These glands produce saliva, which helps lubricate food and begins the digestive process.
Pharynx:
- The pharynx is the throat, and it connects the nasal cavity to the larynx and esophagus.
- It is divided into three parts: the nasopharynx, oropharynx, and laryngopharynx.
- The pharynx plays a vital role in both the digestive and respiratory systems.
Esophagus:
- Also known as the food pipe, the esophagus connects the pharynx to the stomach.
- During swallowing, the epiglottis, a small flap of cartilage, tilts backwards to prevent food from entering the trachea (windpipe).
Stomach:
- The stomach is a muscular organ responsible for mixing food with gastric juices and breaking it down into smaller particles.
- It secretes digestive enzymes, including pepsin, and hydrochloric acid.
- The pyloric sphincter, a ring of muscle at the bottom of the stomach, controls the flow of partially digested food into the duodenum.
Small Intestine:
- The small intestine is the longest part of the digestive tract, divided into three segments: the duodenum, jejunum, and ileum.
- It is where most of the nutrients from food are absorbed into the bloodstream.
- The duodenum receives bile from the gallbladder and pancreatic juice from the pancreas, which aid in digestion.
- The average length of the small intestine in an adult male is 6.9 meters.
Large Intestine:
- Also known as the colon, the large intestine is responsible for absorbing water and electrolytes from undigested food, forming feces.
- It consists of the cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, and anal canal.
- The average length of the large intestine is about 1.5 meters.
Liver:
- The largest internal organ in the human body and the largest gland.
- Located in the upper right quadrant of the abdominal cavity.
- It performs many vital functions, including producing bile, filtering blood, storing glycogen, and synthesizing proteins.
- The liver has four lobes and can be fractured.
- It has an amazing regenerative capacity, capable of growing back from a small portion of itself.
Gallbladder:
- A small, pear-shaped organ located beneath the liver.
- It stores bile produced by the liver, concentrating it and releasing it into the small intestine when needed for fat digestion.
- While the gallbladder isn't essential for life, its removal can lead to digestive issues.
- It is divided into three parts: the fundus, body, and neck.
Pancreas:
- Located behind the stomach, the pancreas is both an exocrine and endocrine gland.
- It secretes digestive enzymes (pancreatic juice) into the small intestine to aid in digestion.
- It also produces several important hormones, including insulin, glucagon, somatostatin, and pancreatic polypeptide.
- Insulin, vital for regulating blood sugar levels, is produced in clusters of cells called the Islets of Langerhans.

Respiratory System

Nasal Cavity:
- The nasal cavity, also called the nasal fossa, is the space inside the nose.
- It is divided into two halves by a vertical wall called the nasal septum.
- Responsible for filtering, warming, and humidifying incoming air.
Larynx:
- Commonly known as the voice box, the larynx is located between the pharynx and the trachea.
- It plays a crucial role in protecting the trachea from foreign objects and in producing sound.
- The thyroid cartilage, the largest cartilage in the larynx, is called the Adam's apple.
Trachea:
- Also known as the windpipe, the trachea is a cartilaginous tube connecting the larynx to the lungs.
- It carries air to and from the lungs.
Bronchi:
- The bronchi are the two main air passages leading from the trachea into the lungs, one to each lung.
- They branch into smaller and smaller airways called bronchioles, eventually leading to tiny air sacs called alveoli where gas exchange occurs.
Lungs:
- The lungs are the primary organs of respiration, responsible for oxygen uptake and carbon dioxide release.
- There are two lungs, the right lung being larger than the left.
- Each lung is divided into lobes (three on the right, two on the left).
- They are protected by the rib cage.
Diaphragm:
- The diaphragm is the primary respiratory muscle, separating the chest cavity from the abdominal cavity.
- Its contraction and relaxation drive breathing, enabling air to enter and leave the lungs.

Urinary System

Kidneys:
- Two bean-shaped organs located in the back of the abdominal cavity.
- They play a crucial role in maintaining fluid and electrolyte balance in the blood.
- They remove waste products from the blood, including urea, creatinine, and excess water.
- They also produce hormones like renin, calcitriol, and erythropoietin, which regulate blood pressure, calcium metabolism, and red blood cell production, respectively.
- The kidneys are composed of millions of microscopic filtration units called nephrons.
Ureters:
- Two narrow tubes that carry urine from the kidneys to the urinary bladder.
Bladder:
- A hollow, muscular organ that stores urine before it is expelled from the body.
- The average bladder can hold between 300 and 500 ml of urine.
Urethra:
- A tube that carries urine from the bladder to the outside of the body.
- The urethra is shorter in females than in males.