Digestive and Respiratory Systems: Anatomy and Functions
Larynx: Anatomy and Function
The larynx is a tubular organ that connects the pharynx to the trachea, located in the front of the neck. During swallowing, communication is intercepted by a layer of cartilage (epiglottis) that prevents food from passing into the airways. It consists of the hyoid bone and the following cartilages:
- Cricoid: It is superimposed on the trachea, forming a ring with an anterior arch and a posterior seal.
- Thyroid: Forms the laryngeal prominence (Adam’s apple).
- Epiglottis: When the larynx descends during swallowing, it is applied against the base of the tongue, closing off the airway.
- Arytenoid: Provides insertion for the vocal process of the vocal cord and the muscular process, where skeletal muscle cartilage is inserted.
- Corniculate and Cuneiform: These are smaller cartilages that support the arytenoids.
Pharynx: Structure and Role in Respiration and Digestion
The pharynx is a muscular tube that aids in breathing and is located in the neck. It connects the nose and mouth with the trachea and esophagus. Since both air and food pass through it, it is part of both the respiratory and digestive tracts. It is supported by the constrictor muscles of the pharynx. The pharynx is lined by a mucous membrane, which varies depending on the area:
- Nasopharynx: Continuously open to the air.
- Oropharynx: Flanked by the palatine tonsils.
- Hypopharynx: Leads to two anatomical tubes: the larynx anteriorly and the esophagus posteriorly.
Esophagus: Structure and Function in Food Transport
The esophagus begins in the neck, passes through the chest, and enters the abdomen through the esophageal hiatus of the diaphragm. Its function is to act as a duct connecting the mouth and stomach, allowing food to reach it. It has the following layers:
- Mucosa: Composed of several layers of cells.
- Muscularis: Contains an inner layer of smooth muscle cells and an outer layer of longitudinal muscle cells, where peristaltic waves form to propel the bolus into the stomach.
It also has two sphincters:
- Lower esophageal sphincter: Located between the esophagus and stomach.
- Upper esophageal sphincter: Located between the pharynx and esophagus.
The esophagus is divided into three parts:
- Cervical
- Thoracic
- Abdominal
Irrigation: Esophageal arteries and veins.
Innervation: Vagus nerve.
Lymphatic drainage: Left gastric lymph nodes.
Stomach: Role in Digestion and Food Storage
The stomach acts as a mixer and a reservoir, ultimately performing enzymatic digestion. It has the following parts:
- Cardia: The opening of the esophagus into the stomach.
- Fundus: The dilated upper portion that relates to the left dome of the diaphragm.
- Body
- Pyloric part: Controls the discharge of gastric contents through the pyloric orifice into the duodenum.
It also has two curvatures:
- Lesser curvature: The shorter, convex edge.
- Greater curvature: The longer edge.
Small Intestine: Absorption of Nutrients
The small intestine is the part of the gut that begins after the stomach and ends at the cecum of the colon. Its primary function is the absorption of nutrients for the human body. One of its important characteristics is the presence of numerous folds that boost the absorptive surface, such as circular folds, villi, and intestinal microvilli. It is divided into three parts:
- Duodenum: The first part of the small intestine. It is composed of muscle fibers, and its concave side fits the pancreas. It starts at the pylorus and ends at the duodenojejunal angle. It is located in the upper and back of the abdomen and has a C-shape comprising four angles describing four portions.
- Jejunum
- Ileum
The end of the small intestine is the terminal ileum, which empties into the cecum through the ileocecal valve. The intestinal wall, besides the usual layers of mucosa, submucosa, muscularis, and serosa, also contains clusters of lymphoid tissue. The entire length of the small intestine is attached to the back wall through the root of the mesentery.
Large Intestine: Water Absorption and Waste Elimination
The large intestine starts from the ileocecal valve in a pouch called the cecum, where the vermiform appendix arises. It is the penultimate portion of the alimentary canal. From the cecum, it describes a series of curves, forming a framework that ends in the rectum and anus. It is divided into the ascending colon, transverse colon, descending colon, and sigmoid colon.
- Cecum: The first portion. Its function is to slow the progression of intestinal contents into the intestine. It has no glands, circular folds, or microvilli. It presents outgrowths.
Function: Absorption of water and nutrients from food, concentration, and storage of solid waste, transforming the chyme into feces to be excreted.
- Rectum: Has a wide cranial portion called the rectal ampulla, which has a great capacity for stretching. The caudal portion is narrower and called the anal canal, where stool accumulates.
- Anus: The anus is the terminal end of the digestive tract. It is a simple hole where the gastrointestinal tract ends, just as the oral cavity is where it begins. It serves as a conduit through which stool passes during defecation.