Learn Chapter 16- Digestion and Absorption with Top Tutors

The liver is a vital organ with numerous functions essential for maintaining overall health and proper bodily function. Some of the key functions of the liver include:

1. Metabolism:

   • Carbohydrate metabolism: The liver helps regulate blood glucose levels by storing excess glucose as glycogen (glycogenesis) and releasing glucose into the bloodstream as needed (glycogenolysis).
   • Lipid metabolism: It synthesizes and metabolizes lipids, including cholesterol and triglycerides, and helps regulate lipid levels in the blood.
   • Protein metabolism: The liver synthesizes plasma proteins, such as albumin and clotting factors, and metabolizes amino acids.

2. Detoxification:

   • The liver plays a central role in detoxifying harmful substances by metabolizing drugs, alcohol, and other toxins.
   • It converts ammonia, a byproduct of protein metabolism, into urea for excretion by the kidneys in the form of urine.

3. Bile Production:

   • The liver produces bile, a greenish-yellow fluid that aids in digestion and absorption of fats in the small intestine.
   • Bile contains bile salts, which emulsify fats, allowing them to be broken down into smaller droplets and digested more efficiently by lipase enzymes.

4. Storage:

   • The liver serves as a storage reservoir for various nutrients and vitamins, including glycogen (stored glucose), fat-soluble vitamins (A, D, E, K), and iron.
   • It also stores blood, which can be released into the bloodstream when needed to maintain blood volume and pressure.

5. Synthesis of Blood Components:

   • The liver synthesizes several important blood components, including clotting factors (such as fibrinogen and prothrombin) and complement proteins involved in the immune response.

6. Immune Function:

   • The liver contains specialized immune cells called Kupffer cells, which help remove pathogens, dead cells, and other debris from the bloodstream.
   • It also produces acute-phase proteins that contribute to the body's immune response to infection and inflammation.

7. Regulation of Hormones:

   • The liver metabolizes and regulates the levels of various hormones, including insulin, glucagon, and thyroid hormones, contributing to overall hormonal balance and metabolic regulation.

Overall, the liver plays a central role in numerous physiological processes essential for maintaining homeostasis and overall health, making it one of the most vital organs in the human body.

The terms "thecodont" and "diphyodont" are both related to the dentition (arrangement and development of teeth) of vertebrates, particularly mammals.

1. Thecodont:

   • The term "thecodont" refers to a type of tooth attachment seen in certain reptiles, particularly archosaurs (a group that includes dinosaurs, crocodiles, and birds). In the thecodont dentition, the teeth are set in sockets or alveoli within the jawbone. Each tooth is firmly anchored in its socket by a periodontal ligament, providing stability and support.
   • Thecodont dentition is characterized by the presence of distinct, individual sockets for each tooth, allowing for efficient chewing and grinding of food. This type of tooth attachment is considered more advanced than other types of attachment seen in reptiles, such as acrodont or pleurodont dentition.
   • Although thecodont dentition is primarily associated with certain reptilian groups, it is also considered the primitive condition from which mammalian teeth, including humans, evolved.

2. Diphyodont:

   • The term "diphyodont" refers to a type of tooth replacement pattern seen in most mammals, including humans. In diphyodont dentition, mammals develop two sets of teeth during their lifetime: a temporary set of deciduous or "milk" teeth, followed by a permanent set of adult teeth.
   • The first set of teeth, known as deciduous teeth or milk teeth, begins to erupt during infancy and typically consists of 20 teeth: 8 incisors, 4 canines, and 8 molars. Deciduous teeth are gradually replaced by permanent teeth as the individual grows and matures.
   • The second set of teeth, known as permanent teeth, consists of 32 teeth in total (in most cases): 8 incisors, 4 canines, 8 premolars, and 12 molars. These permanent teeth replace the deciduous teeth and are typically larger and more durable, designed to last throughout the individual's adult life.
   • The diphyodont dentition pattern allows for the replacement of worn or damaged teeth while maintaining the functionality of the dentition over the lifespan of the mammal.

In summary, "thecodont" refers to a type of tooth attachment seen in certain reptiles where teeth are set in sockets within the jawbone, while "diphyodont" refers to a tooth replacement pattern seen in most mammals, including humans, where two sets of teeth (deciduous and permanent) are developed during the individual's lifetime.

The digestion of proteins begins in the mouth and continues through various stages as food travels through the alimentary canal. Here are the main steps in the digestion of proteins:

1. Mouth:

   • The mechanical breakdown of food begins in the mouth through chewing (mastication), which breaks food into smaller particles, increasing its surface area for enzyme action.
   • Salivary glands secrete saliva containing the enzyme amylase, which initiates the digestion of carbohydrates. However, proteins are not significantly digested in the mouth.

2. Stomach:

   • In the stomach, proteins undergo enzymatic digestion primarily through the action of the enzyme pepsin, which is secreted by gastric glands as inactive pepsinogen.
   • Hydrochloric acid (HCl) secreted by parietal cells in the stomach converts pepsinogen to its active form, pepsin. Pepsin breaks down proteins into smaller peptides by cleaving peptide bonds between specific amino acids.
   • The acidic environment of the stomach (pH around 1.5-2) created by HCl helps denature proteins, unfolding their complex structures and making them more accessible to enzymatic digestion by pepsin.

3. Small Intestine (Duodenum, Jejunum, and Ileum):

   • In the small intestine, the partially digested food mixture, known as chyme, enters the duodenum from the stomach.
   • Pancreatic enzymes, including trypsin, chymotrypsin, and carboxypeptidase, are secreted into the duodenum by the pancreas in response to hormonal signals such as cholecystokinin (CCK) and secretin.
   • These pancreatic enzymes continue the digestion of proteins by breaking down peptides into smaller peptides and individual amino acids. Trypsin specifically hydrolyzes peptide bonds next to positively charged amino acids (arginine and lysine), while chymotrypsin cleaves peptide bonds next to aromatic amino acids (tyrosine, phenylalanine, and tryptophan).
   • Brush border enzymes, such as aminopeptidases and dipeptidases, located on the microvilli of the small intestine, further hydrolyze peptides into amino acids and dipeptides, which can be absorbed by enterocytes (intestinal epithelial cells) lining the small intestine.

4. Absorption:

   • Amino acids, dipeptides, and tripeptides produced by enzymatic digestion of proteins are absorbed across the apical membrane of enterocytes in the small intestine via various transport mechanisms, including active transport and facilitated diffusion.
   • Amino acids are transported across the basolateral membrane of enterocytes into the bloodstream, where they are transported to various tissues for protein synthesis, energy production, and other metabolic processes.

In summary, the digestion of proteins involves the action of various enzymes at different stages of the alimentary canal, including pepsin in the stomach and pancreatic enzymes in the small intestine. Proteins are broken down into peptides, dipeptides, and amino acids, which are then absorbed by enterocytes in the small intestine and transported to tissues for use in various physiological processes.