Human Physiology: Kidney Function, Menopause, Memory, Aging, Digestion
Kidney Function
Kidneys are localized in the retroperitoneal space, one on each side of the spine at the level of vertebrae T12 to L3. The right kidney is slightly lower due to the right lobe of the liver. Kidneys regulate the internal chemical composition through several processes: filtration, absorption, and secretion. Filtration begins in the glomerulus (podocyte), where a filtrate of plasma is formed. This filtrate passes into Bowman’s capsule through hydrostatic pressure. It then passes through the proximal tubule, where the process of urine formation begins, involving reabsorption and secretion. The filtrate then moves through the loop of Henle, where only reabsorption occurs. It passes to the distal tubule, where secretion occurs again, followed by reabsorption in the collecting duct and finally the ureter.
Urination
Urination is triggered by stretch receptors.
Urinalysis (EAS)
Urinalysis is divided into two parts:
- Chemical reactions using a colored strip that reacts with substances in the urine.
- Microscopic visualization of the urine.
Climacteric and Menopause
Climacteric is a transitional period between the fertile and non-fertile phases, extending until after menopause. During this time, the number of follicles and their response to pituitary stimuli decrease, causing menstrual irregularities and decreased frequency of ovulation. The normal pattern of estradiol and progesterone secretion is lost, and levels of both hormones remain low even if ovulation occurs. These levels are lower than those observed before the climacteric. The main change in this phase is an increase in Follicle-Stimulating Hormone (FSH), caused by the decline in inhibin production by the ovaries. Luteinizing Hormone (LH) levels remain normal.
Memory
Memory is the ability to acquire, store, and retrieve information. This information can be stored internally in the brain or externally in artificial devices. There are two main types of memory:
- Declarative memory: This type of memory can be consciously recalled and declared. It is easier to acquire but also easier to forget. This memory system is associated with structures in the medial temporal lobe.
- Non-declarative memory: This includes motor procedures (e.g., riding a bike). This type of memory depends on the basal ganglia (striatum) and requires more time to be acquired and more time to be forgotten.
There are three main types of memory often discussed: photographic, sensory, and emotional.
Factors Related to Memory Loss
- Depression
- Amnesia
- Severe alcoholism
- Repeated head trauma
- Brain injury (e.g., stroke)
Aging
Aging involves the loss of reproductive capacity of somatic cells when telomeres reach a critical level. This leads to a decrease in muscle mass and fibers, muscle denervation, and muscle atrophy. The amount of water in tendons and cartilage decreases, leading to joint stiffness. Brain weight also decreases with aging, caused by neuronal loss.
Digestive System
Digestion begins in the mouth with chewing and the action of amylase. After swallowing, food passes through the pharynx and esophagus into the stomach. Gastric juice, rich in HCl, pepsin, lipase, and rennin, fragments and denatures proteins, acts on some lipids, promotes the absorption of calcium and iron, and kills bacteria, forming chyme. Chyme then enters the small intestine, where most digestion and absorption occur. In the duodenum, proteins are broken down into amino acids, and maltose and some other disaccharides are digested. Pancreatic juice neutralizes the acidity of the chyme. In the jejunum and ileum, intestinal juice enzymes further break down nutrients, which are then absorbed and released into the blood. The remaining food, now a watery, whitish substance called chyle, moves to the large intestine. Here, water and minerals are absorbed, and the undigested material forms stool.