Notes, summaries, assignments, exams, and problems for Biology

Crohn's Disease

Crohn's disease is an inflammatory condition of unknown cause, frequently affecting the ileum in young adults. It causes severe diarrhea with a tendency towards fistulization. It is also known as regional enteritis or terminal ileitis.

Clinical Manifestations

Acute Ileitis

Often confused with appendicitis, acute ileitis occurs in children and adolescents.

Chronic Form

• Insidious onset with diarrhea and fever
• Palpable mass
• Fistulas (20% of cases)

General Symptoms

• Pallor
• Depression
• Erratic polyarthritis

Treatment

Treatment involves a combination of medical and surgical approaches.

Acute Pancreatitis

Concept

Acute pancreatitis is an aseptic inflammation of a necroticohemorrhagic nature. It involves autodigestion of the gland by its own enzymes,... Continue reading "Crohn's Disease, Pancreatitis, and Liver Conditions: Symptoms and Treatment" »

Regulation of Secretion in the Adrenal Cortex

The adrenal cortex is primarily controlled by the hypothalamic-pituitary axis. However, other mechanisms also influence the release of adrenal cortical hormones.

Negative Feedback

The primary feedback mechanism involves the hormone cortisol and its derivative, cortisone. An increase in cortisol levels inhibits Adrenocorticotropic Hormone (ACTH) secretion, while a decrease stimulates it. An excess of cortisol also leads to a decrease in Corticotropin-Releasing Factor (CRF).

Circadian Rhythm

The levels of adrenal cortical hormones are dependent on the circadian rhythm. Cortisol, in particular, exhibits a pronounced circadian rhythm, with the highest levels in the morning and the lowest at night. This rhythm... Continue reading "Adrenal Cortex Hormone Secretion and Regulation" »

Animal Kingdom: Invertebrate Zoology Review

Please review this questionnaire at home. Do not bring it on the day of the exam.

1. All animals are:
   • Autotrophs
2. Which of these animals has radial symmetry?
   • A sea anemone
   • A butterfly
   • A rabbit
   • A snail
3. An animal has bilateral symmetry if…
   • One line can be drawn to divide the animal into halves that are mirror images.
4. How does a cnidarian capture prey?
   • By paralyzing prey with venom.
5. How are coral reefs created?
   • From the skeletons of dead corals.
6. Which of these is a phylum of worms?
   • Annelida
7. Which of these characteristics is shared by all worms?
   • They have a brain.
8. Which of the following describes the feeding behavior of cnidarians?
   • They are carnivores.
9. The bodies of cnidarians have:
   • Radial symmetry.
10. What do earthworms do to soil?

Key Animal Phyla Characteristics

Vertebrates: Backbone & Internal Skeleton

Vertebrates derive their name from the dorsal spine (vertebral column) present in adults, which replaces the embryonic notochord. This structure anchors a rigid internal skeleton, providing essential support and enabling mobility. Vertebrates include several distinct classes:

• Fish: These are aquatic animals that breathe through gills and possess fins for locomotion. While sharks have a skeleton made of cartilage (cartilaginous fish), in most fish species, bone replaces cartilage in adulthood (bony fish).
• Amphibians: Amphibians, such as frogs and salamanders, can inhabit most terrestrial environments. However, they require moist conditions and typically return to water

Fixism

This theory proposes that species do not change; they remain unchanged from their creation. Linnaeus was a proponent of this thought.

Catastrophism

Georges Cuvier proposed that land disasters had destroyed existing species, leading to the creation of new species.

Neutral Theory

This theory posits that chance variations occur in populations, where a mutant gene can be dispersed without any selective advantage.

Punctuated Equilibrium

This theory suggests that the absence of intermediate steps in the fossil record is not due to incompleteness, but rather that evolution sometimes occurs in "leaps."

Evidence of Evolution

• Morphological: Studying comparative anatomy helps to understand the similarities and differences of the same organ in different

The Nephron: Structure and Function

The nephron is the functional and anatomical unit of the kidneys. It is responsible for filtering the blood and reabsorbing essential substances.

Nephron Parts:

1. Bowman's Capsule: The end of the nephron is cup-shaped and surrounds a network of capillaries called the glomerulus. The glomerulus is connected to an afferent arteriole (input) and an efferent arteriole (output).
2. Proximal Convoluted Tubule: Named for its serpentine appearance.
3. Loop of Henle: A narrowed area of the proximal tubule, with a descending and an ascending branch.
4. Distal Convoluted Tubule: A continuation of the loop of Henle, it connects with the collecting duct.

The collecting duct empties into the renal pelvis.

Urine Formation

Urine formation takes... Continue reading "Nephron Function and Urine Formation: A Detailed Look" »

Surgical Enterostomies

Gastrostomy Procedure

For temporary access, a Foley catheter is placed through the abdominal wall into the stomach. The balloon at its end is inflated inside the stomach to secure the tube. Gastrostomy can be used for a long time, with less danger and inconvenience than nasogastric tubes. Complications arise when the tube is dislodged, skin erosion occurs, or there is leakage of gastric contents or formula, causing local infection or peritonitis.

Jejunostomy Procedure

Jejunostomy involves creating a jejunal loop brought to the abdominal wall and inserting a tube into the jejunum through the wall. Surgical jejunostomy also achieves the same reduction in aspiration risk as nasojejunal feeding and less frequently causes erosion... Continue reading "Nutrition Support Methods and Risks" »

Types of Cells in Multicellular Organisms

Diploid Cells

They have two copies of each chromosome type. It is symbolized as 2n. In humans, somatic cells, which constitute the body, have 2x23 chromosomes = 46.

Haploid Cells

They have a single copy of each type of chromosome. It is symbolized as n. In humans, these are the reproductive cells (eggs and sperm) and have 23 chromosomes. n is the number of different types of chromosomes present in each cell.

Mitosis

Inside the life cycle of a cell, we can identify:

• The interphase or growth period, which is the interval between two successive divisions.
• The cell division, the stage where two daughter cells are formed from an initial cell.

Cell Division

Cell division comprises:

1. The division of the nucleus or mitosis,

Understanding Human Veins: Key Drainage Pathways

Veins: The superior vena cava drains the head, neck, upper limbs, and thorax. The inferior vena cava receives blood from the lower limbs, pelvis, and abdomen.

Pulmonary and Cardiac Veins

Pulmonary Veins

There are two pulmonary veins for each lung, and they notably lack valves.

Veins of the Heart

The primary vein of the heart is the coronary sinus.

Detailed Anatomy of Major Veins

Superior Vena Cava

The superior vena cava is formed in the superior mediastinum by the union of the two brachiocephalic veins. It typically measures 2 cm in diameter and 7 cm in length.

Branches of the Superior Vena Cava

• The azygos vein
• Pericardial veins
• Mediastinal veins

Brachiocephalic Veins

These veins represent the union of veins... Continue reading "Human Veins: Anatomy and Venous Drainage Pathways" »

Lower Respiratory System Anatomy

The lower respiratory system includes the trachea, main bronchi, bronchioles, alveoli, lungs, and pleura.

The Trachea

The trachea is a fibrocartilaginous duct that runs from the larynx down to its division into the major bronchi in the chest. This division occurs at a point marked by semi-rigid cartilage called the carina. The trachea is composed of 15 to 20 incomplete hyaline cartilage rings, which are open at the back and connected by fibrous tissue. It is lined by respiratory mucosal tissue.

Bronchi and Bronchioles

The trachea primarily forks into the main bronchi, which enter the lungs through the pulmonary hilum. The right bronchus is longer and more oblique than the left, partly due to the position of the heart.... Continue reading "Anatomy of the Lower Respiratory Tract" »