Anatomy of the Medulla, Liver, Kidneys, and Heart
Medulla Oblongata (Brainstem)
The medulla oblongata, or brainstem myelencephalon, is the lowest of the three segments of the brainstem. It is located between the pons (above) and the spinal cord (below). It takes the form of a truncated cone, approximately three inches long. It is bordered by the spinal cord at the decussation of the pyramids (Mistichèlli). The division with the pons is clear and is marked by the pontomedullary sulcus. However, this division is only visible on the anterior and lateral sides. On the posterior side, the limit is less clear, as it is only half visible and constitutes the upper half of the floor of the 4th ventricle.
Liver
The liver is an organ present in vertebrates and some other animals. It is the largest gland in the body and one of the most important organs in terms of metabolic activity. The liver performs unique and vital functions, such as protein synthesis, detoxification, and storage of vitamins and glycogen. These functions are essential for proper immune function and overall health. It is also responsible for removing substances from the blood that may be harmful to the body, transforming them into harmless substances.
- Form: Resembles the upper half of a horizontal ovoid, very far right, elongated transversely.
- Color: Red-brown.
- Consistency: Friable (brittle).
It comprises a parenchyma surrounded by a thin fibrous capsule called Glisson’s capsule.
Length: In adults, it measures approximately 28 x 15 cm anteroposteriorly and 8 cm in thickness in the right lobe.
Weight: Approximately 1555g.
Kidneys
Humans have two kidneys located at the back of the abdominal cavity. The kidneys contain thousands of small filtering units called nephrons. Each nephron can be divided into two major parts:
- Glomerulus (filtering portion): Filters the blood.
- Tubular/Collecting Duct: Extracts salts, water, and essential nutrients from the filtrate while eliminating waste, mainly urea.
The glomeruli are located near the cortex (surface portion) of the kidneys. They consist of tiny balls of capillaries with very thin walls. These capillaries rest on a substance called the intracellular basement membrane. On the opposite side, the capillary basement membrane is covered by an epithelial ball, forming a cup-like structure known as Bowman’s capsule.
From Bowman’s capsule, a tube called the proximal tubule extends toward the inner medulla (central part) of the kidney. It forms a curve or loop (the loop of Henle) and then returns for a short distance toward the renal cortex. This last segment is called the distal tubule. The distal tubule leads to another tubule of the same name from other nephrons, forming a common collecting duct. Several of these ducts converge in the renal pelvis, located on the inner edge of each kidney. They eventually form the ureters (one for each kidney), which carry urine (water and waste) to the bladder.
The glomerular capillary network is so large that it can hold almost a quarter of all circulating blood at any given time. Approximately 130 ml of blood is filtered every minute.
Sternocleidomastoid Muscle
The sternocleidomastoid muscle is located on the anterolateral aspect of the neck. It originates at the posterior aspect of the manubrium sterni and the medial third of the clavicle. Superiorly, it attaches to the lateral surface of the mastoid process of the temporal bone. It is innervated by the spinal accessory nerve and roots C2 and C3. It functions in lateral flexion and rotation of the head.
Heart
The heart is the main organ of the circulatory system. It is a muscular organ that acts as a suction pump and impeller. It receives blood from the atria (the blood that circulates through the veins) and drives it from the ventricles into the arteries. Valves between the chambers ensure that the blood flows in the correct direction.
The heart is a tapered muscular organ located in the chest cavity. It functions as a pump, pushing blood throughout the body. Slightly larger than a fist, it is divided into four chambers: two upper chambers called atria, and two lower chambers called ventricles. The heart pumps blood through the rhythmic movements of systole and diastole.